(* Title : Lim.ML
Author : Jacques D. Fleuriot
Copyright : 1998 University of Cambridge
Description : Theory of limits, continuity and
differentiation of real=>real functions
*)
val times_divide_eq_right = thm"times_divide_eq_right";
fun ARITH_PROVE str = prove_goal thy str
(fn prems => [cut_facts_tac prems 1,arith_tac 1]);
(*---------------------------------------------------------------
Theory of limits, continuity and differentiation of
real=>real functions
----------------------------------------------------------------*)
Goalw [LIM_def] "(%x. k) -- x --> k";
by Auto_tac;
qed "LIM_const";
Addsimps [LIM_const];
(***-----------------------------------------------------------***)
(*** Some Purely Standard Proofs - Can be used for comparison ***)
(***-----------------------------------------------------------***)
(*---------------
LIM_add
---------------*)
Goalw [LIM_def]
"[| f -- x --> l; g -- x --> m |] ==> (%x. f(x) + g(x)) -- x --> (l + m)";
by (Clarify_tac 1);
by (REPEAT(dres_inst_tac [("x","r/2")] spec 1));
by (Asm_full_simp_tac 1);
by (Clarify_tac 1);
by (res_inst_tac [("R1.0","s"),("R2.0","sa")]
real_linear_less2 1);
by (res_inst_tac [("x","s")] exI 1);
by (res_inst_tac [("x","sa")] exI 2);
by (res_inst_tac [("x","sa")] exI 3);
by Safe_tac;
by (REPEAT(dres_inst_tac [("x","xa")] spec 1)
THEN step_tac (claset() addSEs [order_less_trans]) 1);
by (REPEAT(dres_inst_tac [("x","xa")] spec 2)
THEN step_tac (claset() addSEs [order_less_trans]) 2);
by (REPEAT(dres_inst_tac [("x","xa")] spec 3)
THEN step_tac (claset() addSEs [order_less_trans]) 3);
by (ALLGOALS(rtac (abs_sum_triangle_ineq RS order_le_less_trans)));
by (ALLGOALS(rtac (real_sum_of_halves RS subst)));
by (auto_tac (claset() addIs [real_add_less_mono],simpset()));
qed "LIM_add";
Goalw [LIM_def] "f -- a --> L ==> (%x. -f(x)) -- a --> -L";
by (subgoal_tac "ALL x. abs(- f x + L) = abs(f x + - L)" 1);
by (Asm_full_simp_tac 1);
by (asm_full_simp_tac (simpset() addsimps [real_abs_def]) 1);
qed "LIM_minus";
(*----------------------------------------------
LIM_add_minus
----------------------------------------------*)
Goal "[| f -- x --> l; g -- x --> m |] \
\ ==> (%x. f(x) + -g(x)) -- x --> (l + -m)";
by (blast_tac (claset() addDs [LIM_add,LIM_minus]) 1);
qed "LIM_add_minus";
(*----------------------------------------------
LIM_zero
----------------------------------------------*)
Goal "f -- a --> l ==> (%x. f(x) + -l) -- a --> 0";
by (res_inst_tac [("z1","l")] ((real_add_minus RS subst)) 1);
by (rtac LIM_add_minus 1 THEN Auto_tac);
qed "LIM_zero";
(*--------------------------
Limit not zero
--------------------------*)
Goalw [LIM_def] "k \\<noteq> 0 ==> ~ ((%x. k) -- x --> 0)";
by (res_inst_tac [("R1.0","k"),("R2.0","0")] real_linear_less2 1);
by (auto_tac (claset(), simpset() addsimps [real_abs_def]));
by (res_inst_tac [("x","-k")] exI 1);
by (res_inst_tac [("x","k")] exI 2);
by Auto_tac;
by (ALLGOALS(dres_inst_tac [("y","s")] real_dense));
by Safe_tac;
by (ALLGOALS(res_inst_tac [("x","r + x")] exI));
by Auto_tac;
qed "LIM_not_zero";
(* [| k \\<noteq> 0; (%x. k) -- x --> 0 |] ==> R *)
bind_thm("LIM_not_zeroE", LIM_not_zero RS notE);
Goal "(%x. k) -- x --> L ==> k = L";
by (rtac ccontr 1);
by (dtac LIM_zero 1);
by (rtac LIM_not_zeroE 1 THEN assume_tac 2);
by (arith_tac 1);
qed "LIM_const_eq";
(*------------------------
Limit is Unique
------------------------*)
Goal "[| f -- x --> L; f -- x --> M |] ==> L = M";
by (dtac LIM_minus 1);
by (dtac LIM_add 1 THEN assume_tac 1);
by (auto_tac (claset() addSDs [LIM_const_eq RS sym], simpset()));
qed "LIM_unique";
(*-------------
LIM_mult_zero
-------------*)
Goalw [LIM_def]
"[| f -- x --> 0; g -- x --> 0 |] ==> (%x. f(x)*g(x)) -- x --> 0";
by Safe_tac;
by (dres_inst_tac [("x","1")] spec 1);
by (dres_inst_tac [("x","r")] spec 1);
by (cut_facts_tac [real_zero_less_one] 1);
by (asm_full_simp_tac (simpset() addsimps
[abs_mult]) 1);
by (Clarify_tac 1);
by (res_inst_tac [("R1.0","s"),("R2.0","sa")]
real_linear_less2 1);
by (res_inst_tac [("x","s")] exI 1);
by (res_inst_tac [("x","sa")] exI 2);
by (res_inst_tac [("x","sa")] exI 3);
by Safe_tac;
by (REPEAT(dres_inst_tac [("x","xa")] spec 1)
THEN step_tac (claset() addSEs [order_less_trans]) 1);
by (REPEAT(dres_inst_tac [("x","xa")] spec 2)
THEN step_tac (claset() addSEs [order_less_trans]) 2);
by (REPEAT(dres_inst_tac [("x","xa")] spec 3)
THEN step_tac (claset() addSEs [order_less_trans]) 3);
by (ALLGOALS(res_inst_tac [("t","r")] (real_mult_1 RS subst)));
by (ALLGOALS(rtac abs_mult_less));
by Auto_tac;
qed "LIM_mult_zero";
Goalw [LIM_def] "(%x. x) -- a --> a";
by Auto_tac;
qed "LIM_self";
(*--------------------------------------------------------------
Limits are equal for functions equal except at limit point
--------------------------------------------------------------*)
Goalw [LIM_def]
"[| \\<forall>x. x \\<noteq> a --> (f x = g x) |] \
\ ==> (f -- a --> l) = (g -- a --> l)";
by (auto_tac (claset(), simpset() addsimps [real_add_minus_iff]));
qed "LIM_equal";
Goal "[| (%x. f(x) + -g(x)) -- a --> 0; g -- a --> l |] \
\ ==> f -- a --> l";
by (dtac LIM_add 1 THEN assume_tac 1);
by (auto_tac (claset(), simpset() addsimps [real_add_assoc]));
qed "LIM_trans";
(***-------------------------------------------------------------***)
(*** End of Purely Standard Proofs ***)
(***-------------------------------------------------------------***)
(*--------------------------------------------------------------
Standard and NS definitions of Limit
--------------------------------------------------------------*)
Goalw [LIM_def,NSLIM_def,approx_def]
"f -- x --> L ==> f -- x --NS> L";
by (asm_full_simp_tac
(simpset() addsimps [Infinitesimal_FreeUltrafilterNat_iff]) 1);
by Safe_tac;
by (res_inst_tac [("z","xa")] eq_Abs_hypreal 1);
by (auto_tac (claset(),
simpset() addsimps [real_add_minus_iff, starfun, hypreal_minus,
hypreal_of_real_def, hypreal_add]));
by (rtac bexI 1 THEN rtac lemma_hyprel_refl 2 THEN Step_tac 1);
by (dres_inst_tac [("x","u")] spec 1 THEN Clarify_tac 1);
by (dres_inst_tac [("x","s")] spec 1 THEN Clarify_tac 1);
by (subgoal_tac "\\<forall>n::nat. (xa n) \\<noteq> x & \
\ abs ((xa n) + - x) < s --> abs (f (xa n) + - L) < u" 1);
by (Blast_tac 2);
by (dtac FreeUltrafilterNat_all 1);
by (Ultra_tac 1);
qed "LIM_NSLIM";
(*---------------------------------------------------------------------
Limit: NS definition ==> standard definition
---------------------------------------------------------------------*)
Goal "\\<forall>s. 0 < s --> (\\<exists>xa. xa \\<noteq> x & \
\ abs (xa + - x) < s & r \\<le> abs (f xa + -L)) \
\ ==> \\<forall>n::nat. \\<exists>xa. xa \\<noteq> x & \
\ abs(xa + -x) < inverse(real(Suc n)) & r \\<le> abs(f xa + -L)";
by (Clarify_tac 1);
by (cut_inst_tac [("n1","n")]
(real_of_nat_Suc_gt_zero RS real_inverse_gt_0) 1);
by Auto_tac;
val lemma_LIM = result();
Goal "\\<forall>s. 0 < s --> (\\<exists>xa. xa \\<noteq> x & \
\ abs (xa + - x) < s & r \\<le> abs (f xa + -L)) \
\ ==> \\<exists>X. \\<forall>n::nat. X n \\<noteq> x & \
\ abs(X n + -x) < inverse(real(Suc n)) & r \\<le> abs(f (X n) + -L)";
by (dtac lemma_LIM 1);
by (dtac choice 1);
by (Blast_tac 1);
val lemma_skolemize_LIM2 = result();
Goal "\\<forall>n. X n \\<noteq> x & \
\ abs (X n + - x) < inverse (real(Suc n)) & \
\ r \\<le> abs (f (X n) + - L) ==> \
\ \\<forall>n. abs (X n + - x) < inverse (real(Suc n))";
by (Auto_tac );
val lemma_simp = result();
(*-------------------
NSLIM => LIM
-------------------*)
Goalw [LIM_def,NSLIM_def,approx_def]
"f -- x --NS> L ==> f -- x --> L";
by (asm_full_simp_tac
(simpset() addsimps [Infinitesimal_FreeUltrafilterNat_iff]) 1);
by (EVERY1[Step_tac, rtac ccontr, Asm_full_simp_tac]);
by (fold_tac [real_le_def]);
by (dtac lemma_skolemize_LIM2 1);
by Safe_tac;
by (dres_inst_tac [("x","Abs_hypreal(hyprel``{X})")] spec 1);
by (auto_tac
(claset(),
simpset() addsimps [starfun, hypreal_minus,
hypreal_of_real_def,hypreal_add]));
by (dtac (lemma_simp RS real_seq_to_hypreal_Infinitesimal) 1);
by (asm_full_simp_tac
(simpset() addsimps
[Infinitesimal_FreeUltrafilterNat_iff,hypreal_of_real_def,
hypreal_minus, hypreal_add]) 1);
by (Blast_tac 1);
by (dtac spec 1 THEN dtac mp 1 THEN assume_tac 1);
by (dtac FreeUltrafilterNat_all 1);
by (Ultra_tac 1);
qed "NSLIM_LIM";
(**** Key result ****)
Goal "(f -- x --> L) = (f -- x --NS> L)";
by (blast_tac (claset() addIs [LIM_NSLIM,NSLIM_LIM]) 1);
qed "LIM_NSLIM_iff";
(*-------------------------------------------------------------------*)
(* Proving properties of limits using nonstandard definition and *)
(* hence, the properties hold for standard limits as well *)
(*-------------------------------------------------------------------*)
(*------------------------------------------------
NSLIM_mult and hence (trivially) LIM_mult
------------------------------------------------*)
Goalw [NSLIM_def]
"[| f -- x --NS> l; g -- x --NS> m |] \
\ ==> (%x. f(x) * g(x)) -- x --NS> (l * m)";
by (auto_tac (claset() addSIs [approx_mult_HFinite], simpset()));
qed "NSLIM_mult";
Goal "[| f -- x --> l; g -- x --> m |] \
\ ==> (%x. f(x) * g(x)) -- x --> (l * m)";
by (asm_full_simp_tac (simpset() addsimps [LIM_NSLIM_iff, NSLIM_mult]) 1);
qed "LIM_mult2";
(*----------------------------------------------
NSLIM_add and hence (trivially) LIM_add
Note the much shorter proof
----------------------------------------------*)
Goalw [NSLIM_def]
"[| f -- x --NS> l; g -- x --NS> m |] \
\ ==> (%x. f(x) + g(x)) -- x --NS> (l + m)";
by (auto_tac (claset() addSIs [approx_add], simpset()));
qed "NSLIM_add";
Goal "[| f -- x --> l; g -- x --> m |] \
\ ==> (%x. f(x) + g(x)) -- x --> (l + m)";
by (asm_full_simp_tac (simpset() addsimps [LIM_NSLIM_iff, NSLIM_add]) 1);
qed "LIM_add2";
(*----------------------------------------------
NSLIM_const
----------------------------------------------*)
Goalw [NSLIM_def] "(%x. k) -- x --NS> k";
by Auto_tac;
qed "NSLIM_const";
Addsimps [NSLIM_const];
Goal "(%x. k) -- x --> k";
by (asm_full_simp_tac (simpset() addsimps [LIM_NSLIM_iff]) 1);
qed "LIM_const2";
(*----------------------------------------------
NSLIM_minus
----------------------------------------------*)
Goalw [NSLIM_def]
"f -- a --NS> L ==> (%x. -f(x)) -- a --NS> -L";
by Auto_tac;
qed "NSLIM_minus";
Goal "f -- a --> L ==> (%x. -f(x)) -- a --> -L";
by (asm_full_simp_tac (simpset() addsimps [LIM_NSLIM_iff, NSLIM_minus]) 1);
qed "LIM_minus2";
(*----------------------------------------------
NSLIM_add_minus
----------------------------------------------*)
Goal "[| f -- x --NS> l; g -- x --NS> m |] \
\ ==> (%x. f(x) + -g(x)) -- x --NS> (l + -m)";
by (blast_tac (claset() addDs [NSLIM_add,NSLIM_minus]) 1);
qed "NSLIM_add_minus";
Goal "[| f -- x --> l; g -- x --> m |] \
\ ==> (%x. f(x) + -g(x)) -- x --> (l + -m)";
by (asm_full_simp_tac (simpset() addsimps [LIM_NSLIM_iff,
NSLIM_add_minus]) 1);
qed "LIM_add_minus2";
(*-----------------------------
NSLIM_inverse
-----------------------------*)
Goalw [NSLIM_def]
"[| f -- a --NS> L; L \\<noteq> 0 |] \
\ ==> (%x. inverse(f(x))) -- a --NS> (inverse L)";
by (Clarify_tac 1);
by (dtac spec 1);
by (auto_tac (claset(),
simpset() addsimps [hypreal_of_real_approx_inverse]));
qed "NSLIM_inverse";
Goal "[| f -- a --> L; \
\ L \\<noteq> 0 |] ==> (%x. inverse(f(x))) -- a --> (inverse L)";
by (asm_full_simp_tac (simpset() addsimps [LIM_NSLIM_iff, NSLIM_inverse]) 1);
qed "LIM_inverse";
(*------------------------------
NSLIM_zero
------------------------------*)
Goal "f -- a --NS> l ==> (%x. f(x) + -l) -- a --NS> 0";
by (res_inst_tac [("z1","l")] ((real_add_minus RS subst)) 1);
by (rtac NSLIM_add_minus 1 THEN Auto_tac);
qed "NSLIM_zero";
Goal "f -- a --> l ==> (%x. f(x) + -l) -- a --> 0";
by (asm_full_simp_tac (simpset() addsimps [LIM_NSLIM_iff, NSLIM_zero]) 1);
qed "LIM_zero2";
Goal "(%x. f(x) - l) -- x --NS> 0 ==> f -- x --NS> l";
by (dres_inst_tac [("g","%x. l"),("m","l")] NSLIM_add 1);
by (auto_tac (claset(),simpset() addsimps [real_diff_def, real_add_assoc]));
qed "NSLIM_zero_cancel";
Goal "(%x. f(x) - l) -- x --> 0 ==> f -- x --> l";
by (dres_inst_tac [("g","%x. l"),("m","l")] LIM_add 1);
by (auto_tac (claset(),simpset() addsimps [real_diff_def, real_add_assoc]));
qed "LIM_zero_cancel";
(*--------------------------
NSLIM_not_zero
--------------------------*)
Goalw [NSLIM_def] "k \\<noteq> 0 ==> ~ ((%x. k) -- x --NS> 0)";
by Auto_tac;
by (res_inst_tac [("x","hypreal_of_real x + epsilon")] exI 1);
by (auto_tac (claset() addIs [Infinitesimal_add_approx_self RS approx_sym],
simpset() addsimps [hypreal_epsilon_not_zero]));
qed "NSLIM_not_zero";
(* [| k \\<noteq> 0; (%x. k) -- x --NS> 0 |] ==> R *)
bind_thm("NSLIM_not_zeroE", NSLIM_not_zero RS notE);
Goal "k \\<noteq> 0 ==> ~ ((%x. k) -- x --> 0)";
by (asm_full_simp_tac (simpset() addsimps [LIM_NSLIM_iff, NSLIM_not_zero]) 1);
qed "LIM_not_zero2";
(*-------------------------------------
NSLIM of constant function
-------------------------------------*)
Goal "(%x. k) -- x --NS> L ==> k = L";
by (rtac ccontr 1);
by (dtac NSLIM_zero 1);
by (rtac NSLIM_not_zeroE 1 THEN assume_tac 2);
by (arith_tac 1);
qed "NSLIM_const_eq";
Goal "(%x. k) -- x --> L ==> k = L";
by (asm_full_simp_tac (simpset() addsimps [LIM_NSLIM_iff,
NSLIM_const_eq]) 1);
qed "LIM_const_eq2";
(*------------------------
NS Limit is Unique
------------------------*)
(* can actually be proved more easily by unfolding def! *)
Goal "[| f -- x --NS> L; f -- x --NS> M |] ==> L = M";
by (dtac NSLIM_minus 1);
by (dtac NSLIM_add 1 THEN assume_tac 1);
by (auto_tac (claset() addSDs [NSLIM_const_eq RS sym], simpset()));
qed "NSLIM_unique";
Goal "[| f -- x --> L; f -- x --> M |] ==> L = M";
by (asm_full_simp_tac (simpset() addsimps [LIM_NSLIM_iff, NSLIM_unique]) 1);
qed "LIM_unique2";
(*--------------------
NSLIM_mult_zero
--------------------*)
Goal "[| f -- x --NS> 0; g -- x --NS> 0 |] \
\ ==> (%x. f(x)*g(x)) -- x --NS> 0";
by (dtac NSLIM_mult 1 THEN Auto_tac);
qed "NSLIM_mult_zero";
(* we can use the corresponding thm LIM_mult2 *)
(* for standard definition of limit *)
Goal "[| f -- x --> 0; g -- x --> 0 |] \
\ ==> (%x. f(x)*g(x)) -- x --> 0";
by (dtac LIM_mult2 1 THEN Auto_tac);
qed "LIM_mult_zero2";
(*----------------------------
NSLIM_self
----------------------------*)
Goalw [NSLIM_def] "(%x. x) -- a --NS> a";
by (auto_tac (claset() addIs [starfun_Idfun_approx],simpset()));
qed "NSLIM_self";
Goal "(%x. x) -- a --> a";
by (simp_tac (simpset() addsimps [LIM_NSLIM_iff,NSLIM_self]) 1);
qed "LIM_self2";
(*-----------------------------------------------------------------------------
Derivatives and Continuity - NS and Standard properties
-----------------------------------------------------------------------------*)
(*---------------
Continuity
---------------*)
Goalw [isNSCont_def]
"[| isNSCont f a; y \\<approx> hypreal_of_real a |] \
\ ==> ( *f* f) y \\<approx> hypreal_of_real (f a)";
by (Blast_tac 1);
qed "isNSContD";
Goalw [isNSCont_def,NSLIM_def]
"isNSCont f a ==> f -- a --NS> (f a) ";
by (Blast_tac 1);
qed "isNSCont_NSLIM";
Goalw [isNSCont_def,NSLIM_def]
"f -- a --NS> (f a) ==> isNSCont f a";
by Auto_tac;
by (res_inst_tac [("Q","y = hypreal_of_real a")]
(excluded_middle RS disjE) 1);
by Auto_tac;
qed "NSLIM_isNSCont";
(*-----------------------------------------------------
NS continuity can be defined using NS Limit in
similar fashion to standard def of continuity
-----------------------------------------------------*)
Goal "(isNSCont f a) = (f -- a --NS> (f a))";
by (blast_tac (claset() addIs [isNSCont_NSLIM,NSLIM_isNSCont]) 1);
qed "isNSCont_NSLIM_iff";
(*----------------------------------------------
Hence, NS continuity can be given
in terms of standard limit
---------------------------------------------*)
Goal "(isNSCont f a) = (f -- a --> (f a))";
by (asm_full_simp_tac (simpset() addsimps
[LIM_NSLIM_iff,isNSCont_NSLIM_iff]) 1);
qed "isNSCont_LIM_iff";
(*-----------------------------------------------
Moreover, it's trivial now that NS continuity
is equivalent to standard continuity
-----------------------------------------------*)
Goalw [isCont_def] "(isNSCont f a) = (isCont f a)";
by (rtac isNSCont_LIM_iff 1);
qed "isNSCont_isCont_iff";
(*----------------------------------------
Standard continuity ==> NS continuity
----------------------------------------*)
Goal "isCont f a ==> isNSCont f a";
by (etac (isNSCont_isCont_iff RS iffD2) 1);
qed "isCont_isNSCont";
(*----------------------------------------
NS continuity ==> Standard continuity
----------------------------------------*)
Goal "isNSCont f a ==> isCont f a";
by (etac (isNSCont_isCont_iff RS iffD1) 1);
qed "isNSCont_isCont";
(*--------------------------------------------------------------------------
Alternative definition of continuity
--------------------------------------------------------------------------*)
(* Prove equivalence between NS limits - *)
(* seems easier than using standard def *)
Goalw [NSLIM_def] "(f -- a --NS> L) = ((%h. f(a + h)) -- 0 --NS> L)";
by Auto_tac;
by (dres_inst_tac [("x","hypreal_of_real a + x")] spec 1);
by (dres_inst_tac [("x","-hypreal_of_real a + x")] spec 2);
by Safe_tac;
by (Asm_full_simp_tac 1);
by (rtac ((mem_infmal_iff RS iffD2) RS
(Infinitesimal_add_approx_self RS approx_sym)) 1);
by (rtac (approx_minus_iff2 RS iffD1) 4);
by (asm_full_simp_tac (simpset() addsimps [hypreal_add_commute]) 3);
by (res_inst_tac [("z","x")] eq_Abs_hypreal 2);
by (res_inst_tac [("z","x")] eq_Abs_hypreal 4);
by (auto_tac (claset(),
simpset() addsimps [starfun, hypreal_of_real_def, hypreal_minus,
hypreal_add, real_add_assoc, approx_refl, hypreal_zero_def]));
qed "NSLIM_h_iff";
Goal "(f -- a --NS> f a) = ((%h. f(a + h)) -- 0 --NS> f a)";
by (rtac NSLIM_h_iff 1);
qed "NSLIM_isCont_iff";
Goal "(f -- a --> f a) = ((%h. f(a + h)) -- 0 --> f(a))";
by (simp_tac (simpset() addsimps [LIM_NSLIM_iff, NSLIM_isCont_iff]) 1);
qed "LIM_isCont_iff";
Goalw [isCont_def] "(isCont f x) = ((%h. f(x + h)) -- 0 --> f(x))";
by (simp_tac (simpset() addsimps [LIM_isCont_iff]) 1);
qed "isCont_iff";
(*--------------------------------------------------------------------------
Immediate application of nonstandard criterion for continuity can offer
very simple proofs of some standard property of continuous functions
--------------------------------------------------------------------------*)
(*------------------------
sum continuous
------------------------*)
Goal "[| isCont f a; isCont g a |] ==> isCont (%x. f(x) + g(x)) a";
by (auto_tac (claset() addIs [approx_add],
simpset() addsimps [isNSCont_isCont_iff RS sym, isNSCont_def]));
qed "isCont_add";
(*------------------------
mult continuous
------------------------*)
Goal "[| isCont f a; isCont g a |] ==> isCont (%x. f(x) * g(x)) a";
by (auto_tac (claset() addSIs [starfun_mult_HFinite_approx],
simpset() delsimps [starfun_mult RS sym]
addsimps [isNSCont_isCont_iff RS sym, isNSCont_def]));
qed "isCont_mult";
(*-------------------------------------------
composition of continuous functions
Note very short straightforard proof!
------------------------------------------*)
Goal "[| isCont f a; isCont g (f a) |] \
\ ==> isCont (g o f) a";
by (auto_tac (claset(),simpset() addsimps [isNSCont_isCont_iff RS sym,
isNSCont_def,starfun_o RS sym]));
qed "isCont_o";
Goal "[| isCont f a; isCont g (f a) |] \
\ ==> isCont (%x. g (f x)) a";
by (auto_tac (claset() addDs [isCont_o],simpset() addsimps [o_def]));
qed "isCont_o2";
Goalw [isNSCont_def] "isNSCont f a ==> isNSCont (%x. - f x) a";
by Auto_tac;
qed "isNSCont_minus";
Goal "isCont f a ==> isCont (%x. - f x) a";
by (auto_tac (claset(),simpset() addsimps [isNSCont_isCont_iff RS sym,
isNSCont_minus]));
qed "isCont_minus";
Goalw [isCont_def]
"[| isCont f x; f x \\<noteq> 0 |] ==> isCont (%x. inverse (f x)) x";
by (blast_tac (claset() addIs [LIM_inverse]) 1);
qed "isCont_inverse";
Goal "[| isNSCont f x; f x \\<noteq> 0 |] ==> isNSCont (%x. inverse (f x)) x";
by (auto_tac (claset() addIs [isCont_inverse],simpset() addsimps
[isNSCont_isCont_iff]));
qed "isNSCont_inverse";
Goalw [real_diff_def]
"[| isCont f a; isCont g a |] ==> isCont (%x. f(x) - g(x)) a";
by (auto_tac (claset() addIs [isCont_add,isCont_minus],simpset()));
qed "isCont_diff";
Goalw [isCont_def] "isCont (%x. k) a";
by (Simp_tac 1);
qed "isCont_const";
Addsimps [isCont_const];
Goalw [isNSCont_def] "isNSCont (%x. k) a";
by (Simp_tac 1);
qed "isNSCont_const";
Addsimps [isNSCont_const];
Goalw [isNSCont_def] "isNSCont abs a";
by (auto_tac (claset() addIs [approx_hrabs],
simpset() addsimps [hypreal_of_real_hrabs RS sym,
starfun_rabs_hrabs]));
qed "isNSCont_rabs";
Addsimps [isNSCont_rabs];
Goal "isCont abs a";
by (auto_tac (claset(), simpset() addsimps [isNSCont_isCont_iff RS sym]));
qed "isCont_rabs";
Addsimps [isCont_rabs];
(****************************************************************
(%* Leave as commented until I add topology theory or remove? *%)
(%*------------------------------------------------------------
Elementary topology proof for a characterisation of
continuity now: a function f is continuous if and only
if the inverse image, {x. f(x) \\<in> A}, of any open set A
is always an open set
------------------------------------------------------------*%)
Goal "[| isNSopen A; \\<forall>x. isNSCont f x |] \
\ ==> isNSopen {x. f x \\<in> A}";
by (auto_tac (claset(),simpset() addsimps [isNSopen_iff1]));
by (dtac (mem_monad_approx RS approx_sym) 1);
by (dres_inst_tac [("x","a")] spec 1);
by (dtac isNSContD 1 THEN assume_tac 1);
by (dtac bspec 1 THEN assume_tac 1);
by (dres_inst_tac [("x","( *f* f) x")] approx_mem_monad2 1);
by (blast_tac (claset() addIs [starfun_mem_starset]) 1);
qed "isNSCont_isNSopen";
Goalw [isNSCont_def]
"\\<forall>A. isNSopen A --> isNSopen {x. f x \\<in> A} \
\ ==> isNSCont f x";
by (auto_tac (claset() addSIs [(mem_infmal_iff RS iffD1) RS
(approx_minus_iff RS iffD2)],simpset() addsimps
[Infinitesimal_def,SReal_iff]));
by (dres_inst_tac [("x","{z. abs(z + -f(x)) < ya}")] spec 1);
by (etac (isNSopen_open_interval RSN (2,impE)) 1);
by (auto_tac (claset(),simpset() addsimps [isNSopen_def,isNSnbhd_def]));
by (dres_inst_tac [("x","x")] spec 1);
by (auto_tac (claset() addDs [approx_sym RS approx_mem_monad],
simpset() addsimps [hypreal_of_real_zero RS sym,STAR_starfun_rabs_add_minus]));
qed "isNSopen_isNSCont";
Goal "(\\<forall>x. isNSCont f x) = \
\ (\\<forall>A. isNSopen A --> isNSopen {x. f(x) \\<in> A})";
by (blast_tac (claset() addIs [isNSCont_isNSopen,
isNSopen_isNSCont]) 1);
qed "isNSCont_isNSopen_iff";
(%*------- Standard version of same theorem --------*%)
Goal "(\\<forall>x. isCont f x) = \
\ (\\<forall>A. isopen A --> isopen {x. f(x) \\<in> A})";
by (auto_tac (claset() addSIs [isNSCont_isNSopen_iff],
simpset() addsimps [isNSopen_isopen_iff RS sym,
isNSCont_isCont_iff RS sym]));
qed "isCont_isopen_iff";
*******************************************************************)
(*-----------------------------------------------------------------
Uniform continuity
------------------------------------------------------------------*)
Goalw [isNSUCont_def]
"[| isNSUCont f; x \\<approx> y|] ==> ( *f* f) x \\<approx> ( *f* f) y";
by (Blast_tac 1);
qed "isNSUContD";
Goalw [isUCont_def,isCont_def,LIM_def]
"isUCont f ==> isCont f x";
by (Clarify_tac 1);
by (dtac spec 1);
by (Blast_tac 1);
qed "isUCont_isCont";
Goalw [isNSUCont_def,isUCont_def,approx_def]
"isUCont f ==> isNSUCont f";
by (asm_full_simp_tac (simpset() addsimps
[Infinitesimal_FreeUltrafilterNat_iff]) 1);
by Safe_tac;
by (res_inst_tac [("z","x")] eq_Abs_hypreal 1);
by (res_inst_tac [("z","y")] eq_Abs_hypreal 1);
by (auto_tac (claset(),simpset() addsimps [starfun,
hypreal_minus, hypreal_add]));
by (rtac bexI 1 THEN rtac lemma_hyprel_refl 2 THEN Step_tac 1);
by (dres_inst_tac [("x","u")] spec 1 THEN Clarify_tac 1);
by (dres_inst_tac [("x","s")] spec 1 THEN Clarify_tac 1);
by (subgoal_tac "\\<forall>n::nat. abs ((xa n) + - (xb n)) < s --> abs (f (xa n) + - f (xb n)) < u" 1);
by (Blast_tac 2);
by (thin_tac "\\<forall>x y. abs (x + - y) < s --> abs (f x + - f y) < u" 1);
by (dtac FreeUltrafilterNat_all 1);
by (Ultra_tac 1);
qed "isUCont_isNSUCont";
Goal "\\<forall>s. 0 < s --> (\\<exists>z y. abs (z + - y) < s & r \\<le> abs (f z + -f y)) \
\ ==> \\<forall>n::nat. \\<exists>z y. \
\ abs(z + -y) < inverse(real(Suc n)) & \
\ r \\<le> abs(f z + -f y)";
by (Clarify_tac 1);
by (cut_inst_tac [("n1","n")]
(real_of_nat_Suc_gt_zero RS real_inverse_gt_0) 1);
by Auto_tac;
val lemma_LIMu = result();
Goal "\\<forall>s. 0 < s --> (\\<exists>z y. abs (z + - y) < s & r \\<le> abs (f z + -f y)) \
\ ==> \\<exists>X Y. \\<forall>n::nat. \
\ abs(X n + -(Y n)) < inverse(real(Suc n)) & \
\ r \\<le> abs(f (X n) + -f (Y n))";
by (dtac lemma_LIMu 1);
by (dtac choice 1);
by Safe_tac;
by (dtac choice 1);
by (Blast_tac 1);
val lemma_skolemize_LIM2u = result();
Goal "\\<forall>n. abs (X n + -Y n) < inverse (real(Suc n)) & \
\ r \\<le> abs (f (X n) + - f(Y n)) ==> \
\ \\<forall>n. abs (X n + - Y n) < inverse (real(Suc n))";
by (Auto_tac );
val lemma_simpu = result();
Goalw [isNSUCont_def,isUCont_def,approx_def]
"isNSUCont f ==> isUCont f";
by (asm_full_simp_tac (simpset() addsimps
[Infinitesimal_FreeUltrafilterNat_iff]) 1);
by (EVERY1[Step_tac, rtac ccontr, Asm_full_simp_tac]);
by (fold_tac [real_le_def]);
by (dtac lemma_skolemize_LIM2u 1);
by Safe_tac;
by (dres_inst_tac [("x","Abs_hypreal(hyprel``{X})")] spec 1);
by (dres_inst_tac [("x","Abs_hypreal(hyprel``{Y})")] spec 1);
by (asm_full_simp_tac
(simpset() addsimps [starfun, hypreal_minus,hypreal_add]) 1);
by Auto_tac;
by (dtac (lemma_simpu RS real_seq_to_hypreal_Infinitesimal2) 1);
by (asm_full_simp_tac (simpset() addsimps
[Infinitesimal_FreeUltrafilterNat_iff, hypreal_minus,hypreal_add]) 1);
by (Blast_tac 1);
by (rotate_tac 2 1);
by (dres_inst_tac [("x","r")] spec 1);
by (Clarify_tac 1);
by (dtac FreeUltrafilterNat_all 1);
by (Ultra_tac 1);
qed "isNSUCont_isUCont";
(*------------------------------------------------------------------
Derivatives
------------------------------------------------------------------*)
Goalw [deriv_def]
"(DERIV f x :> D) = ((%h. (f(x + h) + - f(x))/h) -- 0 --> D)";
by (Blast_tac 1);
qed "DERIV_iff";
Goalw [deriv_def]
"(DERIV f x :> D) = ((%h. (f(x + h) + - f(x))/h) -- 0 --NS> D)";
by (simp_tac (simpset() addsimps [LIM_NSLIM_iff]) 1);
qed "DERIV_NS_iff";
Goalw [deriv_def]
"DERIV f x :> D \
\ ==> (%h. (f(x + h) + - f(x))/h) -- 0 --> D";
by (Blast_tac 1);
qed "DERIVD";
Goalw [deriv_def] "DERIV f x :> D ==> \
\ (%h. (f(x + h) + - f(x))/h) -- 0 --NS> D";
by (asm_full_simp_tac (simpset() addsimps [LIM_NSLIM_iff]) 1);
qed "NS_DERIVD";
(* Uniqueness *)
Goalw [deriv_def]
"[| DERIV f x :> D; DERIV f x :> E |] ==> D = E";
by (blast_tac (claset() addIs [LIM_unique]) 1);
qed "DERIV_unique";
Goalw [nsderiv_def]
"[| NSDERIV f x :> D; NSDERIV f x :> E |] ==> D = E";
by (cut_facts_tac [Infinitesimal_epsilon, hypreal_epsilon_not_zero] 1);
by (auto_tac (claset() addSDs [inst "x" "epsilon" bspec]
addSIs [inj_hypreal_of_real RS injD]
addDs [approx_trans3],
simpset()));
qed "NSDeriv_unique";
(*------------------------------------------------------------------------
Differentiable
------------------------------------------------------------------------*)
Goalw [differentiable_def]
"f differentiable x ==> \\<exists>D. DERIV f x :> D";
by (assume_tac 1);
qed "differentiableD";
Goalw [differentiable_def]
"DERIV f x :> D ==> f differentiable x";
by (Blast_tac 1);
qed "differentiableI";
Goalw [NSdifferentiable_def]
"f NSdifferentiable x ==> \\<exists>D. NSDERIV f x :> D";
by (assume_tac 1);
qed "NSdifferentiableD";
Goalw [NSdifferentiable_def]
"NSDERIV f x :> D ==> f NSdifferentiable x";
by (Blast_tac 1);
qed "NSdifferentiableI";
(*--------------------------------------------------------
Alternative definition for differentiability
-------------------------------------------------------*)
Goalw [LIM_def]
"((%h. (f(a + h) + - f(a))/h) -- 0 --> D) = \
\ ((%x. (f(x) + -f(a)) / (x + -a)) -- a --> D)";
by Safe_tac;
by (ALLGOALS(dtac spec));
by Safe_tac;
by (Blast_tac 1 THEN Blast_tac 2);
by (ALLGOALS(res_inst_tac [("x","s")] exI));
by Safe_tac;
by (dres_inst_tac [("x","x + -a")] spec 1);
by (dres_inst_tac [("x","x + a")] spec 2);
by (auto_tac (claset(), simpset() addsimps real_add_ac));
qed "DERIV_LIM_iff";
Goalw [deriv_def] "(DERIV f x :> D) = \
\ ((%z. (f(z) + -f(x)) / (z + -x)) -- x --> D)";
by (simp_tac (simpset() addsimps [DERIV_LIM_iff]) 1);
qed "DERIV_iff2";
(*--------------------------------------------------------
Equivalence of NS and standard defs of differentiation
-------------------------------------------------------*)
(*-------------------------------------------
First NSDERIV in terms of NSLIM
-------------------------------------------*)
(*--- first equivalence ---*)
Goalw [nsderiv_def,NSLIM_def]
"(NSDERIV f x :> D) = ((%h. (f(x + h) + - f(x))/h) -- 0 --NS> D)";
by Auto_tac;
by (dres_inst_tac [("x","xa")] bspec 1);
by (rtac ccontr 3);
by (dres_inst_tac [("x","h")] spec 3);
by (auto_tac (claset(),
simpset() addsimps [mem_infmal_iff, starfun_lambda_cancel]));
qed "NSDERIV_NSLIM_iff";
(*--- second equivalence ---*)
Goal "(NSDERIV f x :> D) = \
\ ((%z. (f(z) + -f(x)) / (z + -x)) -- x --NS> D)";
by (full_simp_tac (simpset() addsimps
[NSDERIV_NSLIM_iff, DERIV_LIM_iff, LIM_NSLIM_iff RS sym]) 1);
qed "NSDERIV_NSLIM_iff2";
(* while we're at it! *)
Goalw [real_diff_def]
"(NSDERIV f x :> D) = \
\ (\\<forall>xa. \
\ xa \\<noteq> hypreal_of_real x & xa \\<approx> hypreal_of_real x --> \
\ ( *f* (%z. (f z - f x) / (z - x))) xa \\<approx> hypreal_of_real D)";
by (auto_tac (claset(), simpset() addsimps [NSDERIV_NSLIM_iff2, NSLIM_def]));
qed "NSDERIV_iff2";
Goal "(NSDERIV f x :> D) ==> \
\ (\\<forall>u. \
\ u \\<approx> hypreal_of_real x --> \
\ ( *f* (%z. f z - f x)) u \\<approx> hypreal_of_real D * (u - hypreal_of_real x))";
by (auto_tac (claset(), simpset() addsimps [NSDERIV_iff2]));
by (case_tac "u = hypreal_of_real x" 1);
by (auto_tac (claset(), simpset() addsimps [hypreal_diff_def]));
by (dres_inst_tac [("x","u")] spec 1);
by Auto_tac;
by (dres_inst_tac [("c","u - hypreal_of_real x"),("b","hypreal_of_real D")]
approx_mult1 1);
by (ALLGOALS(dtac (hypreal_not_eq_minus_iff RS iffD1)));
by (subgoal_tac "( *f* (%z. z - x)) u \\<noteq> (0::hypreal)" 2);
by (auto_tac (claset(),
simpset() addsimps [real_diff_def, hypreal_diff_def,
(approx_minus_iff RS iffD1) RS (mem_infmal_iff RS iffD2),
Infinitesimal_subset_HFinite RS subsetD]));
qed "NSDERIVD5";
Goal "(NSDERIV f x :> D) ==> \
\ (\\<forall>h \\<in> Infinitesimal. \
\ (( *f* f)(hypreal_of_real x + h) - \
\ hypreal_of_real (f x))\\<approx> (hypreal_of_real D) * h)";
by (auto_tac (claset(),simpset() addsimps [nsderiv_def]));
by (case_tac "h = (0::hypreal)" 1);
by (auto_tac (claset(),simpset() addsimps [hypreal_diff_def]));
by (dres_inst_tac [("x","h")] bspec 1);
by (dres_inst_tac [("c","h")] approx_mult1 2);
by (auto_tac (claset() addIs [Infinitesimal_subset_HFinite RS subsetD],
simpset() addsimps [hypreal_diff_def]));
qed "NSDERIVD4";
Goal "(NSDERIV f x :> D) ==> \
\ (\\<forall>h \\<in> Infinitesimal - {0}. \
\ (( *f* f)(hypreal_of_real x + h) - \
\ hypreal_of_real (f x))\\<approx> (hypreal_of_real D) * h)";
by (auto_tac (claset(),simpset() addsimps [nsderiv_def]));
by (rtac ccontr 1 THEN dres_inst_tac [("x","h")] bspec 1);
by (dres_inst_tac [("c","h")] approx_mult1 2);
by (auto_tac (claset() addIs [Infinitesimal_subset_HFinite RS subsetD],
simpset() addsimps [hypreal_mult_assoc, hypreal_diff_def]));
qed "NSDERIVD3";
(*--------------------------------------------------------------
Now equivalence between NSDERIV and DERIV
-------------------------------------------------------------*)
Goalw [deriv_def] "(NSDERIV f x :> D) = (DERIV f x :> D)";
by (simp_tac (simpset() addsimps [NSDERIV_NSLIM_iff,LIM_NSLIM_iff]) 1);
qed "NSDERIV_DERIV_iff";
(*---------------------------------------------------
Differentiability implies continuity
nice and simple "algebraic" proof
--------------------------------------------------*)
Goalw [nsderiv_def]
"NSDERIV f x :> D ==> isNSCont f x";
by (auto_tac (claset(),simpset() addsimps
[isNSCont_NSLIM_iff,NSLIM_def]));
by (dtac (approx_minus_iff RS iffD1) 1);
by (dtac (hypreal_not_eq_minus_iff RS iffD1) 1);
by (dres_inst_tac [("x","-hypreal_of_real x + xa")] bspec 1);
by (asm_full_simp_tac (simpset() addsimps
[hypreal_add_assoc RS sym]) 2);
by (auto_tac (claset(),simpset() addsimps
[mem_infmal_iff RS sym,hypreal_add_commute]));
by (dres_inst_tac [("c","xa + -hypreal_of_real x")] approx_mult1 1);
by (auto_tac (claset() addIs [Infinitesimal_subset_HFinite
RS subsetD],simpset() addsimps [hypreal_mult_assoc]));
by (dres_inst_tac [("x3","D")] (HFinite_hypreal_of_real RSN
(2,Infinitesimal_HFinite_mult) RS (mem_infmal_iff RS iffD1)) 1);
by (blast_tac (claset() addIs [approx_trans,
hypreal_mult_commute RS subst,
(approx_minus_iff RS iffD2)]) 1);
qed "NSDERIV_isNSCont";
(* Now Sandard proof *)
Goal "DERIV f x :> D ==> isCont f x";
by (asm_full_simp_tac (simpset() addsimps
[NSDERIV_DERIV_iff RS sym, isNSCont_isCont_iff RS sym,
NSDERIV_isNSCont]) 1);
qed "DERIV_isCont";
(*----------------------------------------------------------------------------
Differentiation rules for combinations of functions
follow from clear, straightforard, algebraic
manipulations
----------------------------------------------------------------------------*)
(*-------------------------
Constant function
------------------------*)
(* use simple constant nslimit theorem *)
Goal "(NSDERIV (%x. k) x :> 0)";
by (simp_tac (simpset() addsimps [NSDERIV_NSLIM_iff]) 1);
qed "NSDERIV_const";
Addsimps [NSDERIV_const];
Goal "(DERIV (%x. k) x :> 0)";
by (simp_tac (simpset() addsimps [NSDERIV_DERIV_iff RS sym]) 1);
qed "DERIV_const";
Addsimps [DERIV_const];
(*-----------------------------------------------------
Sum of functions- proved easily
----------------------------------------------------*)
Goal "[| NSDERIV f x :> Da; NSDERIV g x :> Db |] \
\ ==> NSDERIV (%x. f x + g x) x :> Da + Db";
by (asm_full_simp_tac (simpset() addsimps [NSDERIV_NSLIM_iff,
NSLIM_def]) 1 THEN REPEAT (Step_tac 1));
by (auto_tac (claset(),
simpset() addsimps [hypreal_add_divide_distrib]));
by (dres_inst_tac [("b","hypreal_of_real Da"),
("d","hypreal_of_real Db")] approx_add 1);
by (auto_tac (claset(), simpset() addsimps hypreal_add_ac));
qed "NSDERIV_add";
(* Standard theorem *)
Goal "[| DERIV f x :> Da; DERIV g x :> Db |] \
\ ==> DERIV (%x. f x + g x) x :> Da + Db";
by (asm_full_simp_tac (simpset() addsimps [NSDERIV_add,
NSDERIV_DERIV_iff RS sym]) 1);
qed "DERIV_add";
(*-----------------------------------------------------
Product of functions - Proof is trivial but tedious
and long due to rearrangement of terms
----------------------------------------------------*)
Goal "((a::hypreal)*b) + -(c*d) = (b*(a + -c)) + (c*(b + -d))";
by (simp_tac (simpset() addsimps [hypreal_add_mult_distrib2]) 1);
val lemma_nsderiv1 = result();
Goal "[| (x + y) / z = hypreal_of_real D + yb; z \\<noteq> 0; \
\ z \\<in> Infinitesimal; yb \\<in> Infinitesimal |] \
\ ==> x + y \\<approx> 0";
by (forw_inst_tac [("c1","z")] (hypreal_mult_right_cancel RS iffD2) 1
THEN assume_tac 1);
by (thin_tac "(x + y) / z = hypreal_of_real D + yb" 1);
by (auto_tac (claset() addSIs [Infinitesimal_HFinite_mult2, HFinite_add],
simpset() addsimps [hypreal_mult_assoc, mem_infmal_iff RS sym]));
by (etac (Infinitesimal_subset_HFinite RS subsetD) 1);
val lemma_nsderiv2 = result();
Goal "[| NSDERIV f x :> Da; NSDERIV g x :> Db |] \
\ ==> NSDERIV (%x. f x * g x) x :> (Da * g(x)) + (Db * f(x))";
by (asm_full_simp_tac (simpset() addsimps [NSDERIV_NSLIM_iff, NSLIM_def]) 1);
by (REPEAT (Step_tac 1));
by (auto_tac (claset(),
simpset() addsimps [starfun_lambda_cancel, lemma_nsderiv1]));
by (simp_tac (simpset() addsimps [hypreal_add_divide_distrib]) 1);
by (REPEAT(dtac (bex_Infinitesimal_iff2 RS iffD2) 1));
by (auto_tac (claset(),
simpset() delsimps [hypreal_times_divide1_eq]
addsimps [hypreal_times_divide1_eq RS sym]));
by (dres_inst_tac [("D","Db")] lemma_nsderiv2 1);
by (dtac (approx_minus_iff RS iffD2 RS (bex_Infinitesimal_iff2 RS iffD2)) 4);
by (auto_tac (claset() addSIs [approx_add_mono1],
simpset() addsimps [hypreal_add_mult_distrib, hypreal_add_mult_distrib2,
hypreal_mult_commute, hypreal_add_assoc]));
by (res_inst_tac [("w1","hypreal_of_real Db * hypreal_of_real (f x)")]
(hypreal_add_commute RS subst) 1);
by (auto_tac (claset() addSIs [Infinitesimal_add_approx_self2 RS approx_sym,
Infinitesimal_add, Infinitesimal_mult,
Infinitesimal_hypreal_of_real_mult,
Infinitesimal_hypreal_of_real_mult2],
simpset() addsimps [hypreal_add_assoc RS sym]));
qed "NSDERIV_mult";
Goal "[| DERIV f x :> Da; DERIV g x :> Db |] \
\ ==> DERIV (%x. f x * g x) x :> (Da * g(x)) + (Db * f(x))";
by (asm_full_simp_tac (simpset() addsimps [NSDERIV_mult,
NSDERIV_DERIV_iff RS sym]) 1);
qed "DERIV_mult";
(*----------------------------
Multiplying by a constant
---------------------------*)
Goal "NSDERIV f x :> D \
\ ==> NSDERIV (%x. c * f x) x :> c*D";
by (asm_full_simp_tac
(simpset() addsimps [times_divide_eq_right RS sym, NSDERIV_NSLIM_iff,
real_minus_mult_eq2, real_add_mult_distrib2 RS sym]
delsimps [times_divide_eq_right, real_mult_minus_eq2]) 1);
by (etac (NSLIM_const RS NSLIM_mult) 1);
qed "NSDERIV_cmult";
(* let's do the standard proof though theorem *)
(* LIM_mult2 follows from a NS proof *)
Goalw [deriv_def]
"DERIV f x :> D \
\ ==> DERIV (%x. c * f x) x :> c*D";
by (asm_full_simp_tac
(simpset() addsimps [times_divide_eq_right RS sym, NSDERIV_NSLIM_iff,
real_minus_mult_eq2, real_add_mult_distrib2 RS sym]
delsimps [times_divide_eq_right, real_mult_minus_eq2]) 1);
by (etac (LIM_const RS LIM_mult2) 1);
qed "DERIV_cmult";
(*--------------------------------
Negation of function
-------------------------------*)
Goal "NSDERIV f x :> D ==> NSDERIV (%x. -(f x)) x :> -D";
by (asm_full_simp_tac (simpset() addsimps [NSDERIV_NSLIM_iff]) 1);
by (dtac NSLIM_minus 1);
by (subgoal_tac "ALL a::real. ALL b. - a + b = - (a + - b)" 1);
by (asm_full_simp_tac (HOL_ss addsimps [thm"minus_divide_left" RS sym]) 1);
by (Asm_full_simp_tac 1);
qed "NSDERIV_minus";
Goal "DERIV f x :> D \
\ ==> DERIV (%x. -(f x)) x :> -D";
by (asm_full_simp_tac (simpset() addsimps
[NSDERIV_minus,NSDERIV_DERIV_iff RS sym]) 1);
qed "DERIV_minus";
(*-------------------------------
Subtraction
------------------------------*)
Goal "[| NSDERIV f x :> Da; NSDERIV g x :> Db |] \
\ ==> NSDERIV (%x. f x + -g x) x :> Da + -Db";
by (blast_tac (claset() addDs [NSDERIV_add,NSDERIV_minus]) 1);
qed "NSDERIV_add_minus";
Goal "[| DERIV f x :> Da; DERIV g x :> Db |] \
\ ==> DERIV (%x. f x + -g x) x :> Da + -Db";
by (blast_tac (claset() addDs [DERIV_add,DERIV_minus]) 1);
qed "DERIV_add_minus";
Goalw [real_diff_def]
"[| NSDERIV f x :> Da; NSDERIV g x :> Db |] \
\ ==> NSDERIV (%x. f x - g x) x :> Da - Db";
by (blast_tac (claset() addIs [NSDERIV_add_minus]) 1);
qed "NSDERIV_diff";
Goalw [real_diff_def]
"[| DERIV f x :> Da; DERIV g x :> Db |] \
\ ==> DERIV (%x. f x - g x) x :> Da - Db";
by (blast_tac (claset() addIs [DERIV_add_minus]) 1);
qed "DERIV_diff";
(*---------------------------------------------------------------
(NS) Increment
---------------------------------------------------------------*)
Goalw [increment_def]
"f NSdifferentiable x ==> \
\ increment f x h = ( *f* f) (hypreal_of_real(x) + h) + \
\ -hypreal_of_real (f x)";
by (Blast_tac 1);
qed "incrementI";
Goal "NSDERIV f x :> D ==> \
\ increment f x h = ( *f* f) (hypreal_of_real(x) + h) + \
\ -hypreal_of_real (f x)";
by (etac (NSdifferentiableI RS incrementI) 1);
qed "incrementI2";
(* The Increment theorem -- Keisler p. 65 *)
Goal "[| NSDERIV f x :> D; h \\<in> Infinitesimal; h \\<noteq> 0 |] \
\ ==> \\<exists>e \\<in> Infinitesimal. increment f x h = hypreal_of_real(D)*h + e*h";
by (forw_inst_tac [("h","h")] incrementI2 1 THEN rewtac nsderiv_def);
by (dtac bspec 1 THEN Auto_tac);
by (dtac (bex_Infinitesimal_iff2 RS iffD2) 1 THEN Step_tac 1);
by (forw_inst_tac [("b1","hypreal_of_real(D) + y")]
((hypreal_mult_right_cancel RS iffD2)) 1);
by (thin_tac "(( *f* f) (hypreal_of_real(x) + h) + \
\ - hypreal_of_real (f x)) / h = hypreal_of_real(D) + y" 2);
by (assume_tac 1);
by (asm_full_simp_tac (simpset() addsimps [hypreal_times_divide1_eq RS sym]
delsimps [hypreal_times_divide1_eq]) 1);
by (auto_tac (claset(),
simpset() addsimps [hypreal_add_mult_distrib]));
qed "increment_thm";
Goal "[| NSDERIV f x :> D; h \\<approx> 0; h \\<noteq> 0 |] \
\ ==> \\<exists>e \\<in> Infinitesimal. increment f x h = \
\ hypreal_of_real(D)*h + e*h";
by (blast_tac (claset() addSDs [mem_infmal_iff RS iffD2]
addSIs [increment_thm]) 1);
qed "increment_thm2";
Goal "[| NSDERIV f x :> D; h \\<approx> 0; h \\<noteq> 0 |] \
\ ==> increment f x h \\<approx> 0";
by (dtac increment_thm2 1 THEN auto_tac (claset() addSIs
[Infinitesimal_HFinite_mult2,HFinite_add],simpset() addsimps
[hypreal_add_mult_distrib RS sym,mem_infmal_iff RS sym]));
by (etac (Infinitesimal_subset_HFinite RS subsetD) 1);
qed "increment_approx_zero";
(*---------------------------------------------------------------
Similarly to the above, the chain rule admits an entirely
straightforward derivation. Compare this with Harrison's
HOL proof of the chain rule, which proved to be trickier and
required an alternative characterisation of differentiability-
the so-called Carathedory derivative. Our main problem is
manipulation of terms.
--------------------------------------------------------------*)
(* lemmas *)
Goalw [nsderiv_def]
"[| NSDERIV g x :> D; \
\ ( *f* g) (hypreal_of_real(x) + xa) = hypreal_of_real(g x);\
\ xa \\<in> Infinitesimal;\
\ xa \\<noteq> 0 \
\ |] ==> D = 0";
by (dtac bspec 1);
by Auto_tac;
qed "NSDERIV_zero";
(* can be proved differently using NSLIM_isCont_iff *)
Goalw [nsderiv_def]
"[| NSDERIV f x :> D; h \\<in> Infinitesimal; h \\<noteq> 0 |] \
\ ==> ( *f* f) (hypreal_of_real(x) + h) + -hypreal_of_real(f x) \\<approx> 0";
by (asm_full_simp_tac (simpset() addsimps
[mem_infmal_iff RS sym]) 1);
by (rtac Infinitesimal_ratio 1);
by (rtac approx_hypreal_of_real_HFinite 3);
by Auto_tac;
qed "NSDERIV_approx";
(*---------------------------------------------------------------
from one version of differentiability
f(x) - f(a)
--------------- \\<approx> Db
x - a
---------------------------------------------------------------*)
Goal "[| NSDERIV f (g x) :> Da; \
\ ( *f* g) (hypreal_of_real(x) + xa) \\<noteq> hypreal_of_real (g x); \
\ ( *f* g) (hypreal_of_real(x) + xa) \\<approx> hypreal_of_real (g x) \
\ |] ==> (( *f* f) (( *f* g) (hypreal_of_real(x) + xa)) \
\ + - hypreal_of_real (f (g x))) \
\ / (( *f* g) (hypreal_of_real(x) + xa) + - hypreal_of_real (g x)) \
\ \\<approx> hypreal_of_real(Da)";
by (auto_tac (claset(),
simpset() addsimps [NSDERIV_NSLIM_iff2, NSLIM_def]));
qed "NSDERIVD1";
(*--------------------------------------------------------------
from other version of differentiability
f(x + h) - f(x)
----------------- \\<approx> Db
h
--------------------------------------------------------------*)
Goal "[| NSDERIV g x :> Db; xa \\<in> Infinitesimal; xa \\<noteq> 0 |] \
\ ==> (( *f* g) (hypreal_of_real(x) + xa) + - hypreal_of_real(g x)) / xa \
\ \\<approx> hypreal_of_real(Db)";
by (auto_tac (claset(),
simpset() addsimps [NSDERIV_NSLIM_iff, NSLIM_def,
mem_infmal_iff, starfun_lambda_cancel]));
qed "NSDERIVD2";
Goal "(z::hypreal) \\<noteq> 0 ==> x*y = (x*inverse(z))*(z*y)";
by Auto_tac;
qed "lemma_chain";
(*------------------------------------------------------
This proof uses both definitions of differentiability.
------------------------------------------------------*)
Goal "[| NSDERIV f (g x) :> Da; NSDERIV g x :> Db |] \
\ ==> NSDERIV (f o g) x :> Da * Db";
by (asm_simp_tac (simpset() addsimps [NSDERIV_NSLIM_iff,
NSLIM_def,mem_infmal_iff RS sym]) 1 THEN Step_tac 1);
by (forw_inst_tac [("f","g")] NSDERIV_approx 1);
by (auto_tac (claset(),
simpset() addsimps [starfun_lambda_cancel2, starfun_o RS sym]));
by (case_tac "( *f* g) (hypreal_of_real(x) + xa) = hypreal_of_real (g x)" 1);
by (dres_inst_tac [("g","g")] NSDERIV_zero 1);
by (auto_tac (claset(), simpset() addsimps [hypreal_divide_def]));
by (res_inst_tac [("z1","( *f* g) (hypreal_of_real(x) + xa) + -hypreal_of_real (g x)"),
("y1","inverse xa")] (lemma_chain RS ssubst) 1);
by (etac (hypreal_not_eq_minus_iff RS iffD1) 1);
by (rtac approx_mult_hypreal_of_real 1);
by (fold_tac [hypreal_divide_def]);
by (blast_tac (claset() addIs [NSDERIVD1,
approx_minus_iff RS iffD2]) 1);
by (blast_tac (claset() addIs [NSDERIVD2]) 1);
qed "NSDERIV_chain";
(* standard version *)
Goal "[| DERIV f (g x) :> Da; \
\ DERIV g x :> Db \
\ |] ==> DERIV (f o g) x :> Da * Db";
by (asm_full_simp_tac (simpset() addsimps [NSDERIV_DERIV_iff RS sym,
NSDERIV_chain]) 1);
qed "DERIV_chain";
Goal "[| DERIV f (g x) :> Da; DERIV g x :> Db |] \
\ ==> DERIV (%x. f (g x)) x :> Da * Db";
by (auto_tac (claset() addDs [DERIV_chain], simpset() addsimps [o_def]));
qed "DERIV_chain2";
(*------------------------------------------------------------------
Differentiation of natural number powers
------------------------------------------------------------------*)
Goal "NSDERIV (%x. x) x :> 1";
by (auto_tac (claset(),
simpset() addsimps [NSDERIV_NSLIM_iff, NSLIM_def ,starfun_Id]));
qed "NSDERIV_Id";
Addsimps [NSDERIV_Id];
(*derivative of the identity function*)
Goal "DERIV (%x. x) x :> 1";
by (simp_tac (simpset() addsimps [NSDERIV_DERIV_iff RS sym]) 1);
qed "DERIV_Id";
Addsimps [DERIV_Id];
bind_thm ("isCont_Id", DERIV_Id RS DERIV_isCont);
(*derivative of linear multiplication*)
Goal "DERIV (op * c) x :> c";
by (cut_inst_tac [("c","c"),("x","x")] (DERIV_Id RS DERIV_cmult) 1);
by (Asm_full_simp_tac 1);
qed "DERIV_cmult_Id";
Addsimps [DERIV_cmult_Id];
Goal "NSDERIV (op * c) x :> c";
by (simp_tac (simpset() addsimps [NSDERIV_DERIV_iff]) 1);
qed "NSDERIV_cmult_Id";
Addsimps [NSDERIV_cmult_Id];
Goal "DERIV (%x. x ^ n) x :> real n * (x ^ (n - Suc 0))";
by (induct_tac "n" 1);
by (dtac (DERIV_Id RS DERIV_mult) 2);
by (auto_tac (claset(),
simpset() addsimps [real_of_nat_Suc, real_add_mult_distrib]));
by (case_tac "0 < n" 1);
by (dres_inst_tac [("x","x")] realpow_minus_mult 1);
by (auto_tac (claset(),
simpset() addsimps [real_mult_assoc, real_add_commute]));
qed "DERIV_pow";
(* NS version *)
Goal "NSDERIV (%x. x ^ n) x :> real n * (x ^ (n - Suc 0))";
by (simp_tac (simpset() addsimps [NSDERIV_DERIV_iff, DERIV_pow]) 1);
qed "NSDERIV_pow";
(*---------------------------------------------------------------
Power of -1
---------------------------------------------------------------*)
(*Can't get rid of x \\<noteq> 0 because it isn't continuous at zero*)
Goalw [nsderiv_def]
"x \\<noteq> 0 ==> NSDERIV (%x. inverse(x)) x :> (- (inverse x ^ Suc (Suc 0)))";
by (rtac ballI 1 THEN Asm_full_simp_tac 1 THEN Step_tac 1);
by (ftac Infinitesimal_add_not_zero 1);
by (asm_full_simp_tac (simpset() addsimps [hypreal_add_commute]) 2);
by (auto_tac (claset(),
simpset() addsimps [starfun_inverse_inverse, realpow_two]
delsimps [hypreal_minus_mult_eq1 RS sym,
hypreal_minus_mult_eq2 RS sym]));
by (asm_full_simp_tac
(simpset() addsimps [hypreal_inverse_add,
hypreal_inverse_distrib RS sym, hypreal_minus_inverse RS sym]
@ hypreal_add_ac @ hypreal_mult_ac
delsimps [hypreal_minus_mult_eq1 RS sym,
hypreal_minus_mult_eq2 RS sym] ) 1);
by (asm_simp_tac (simpset() addsimps [hypreal_mult_assoc RS sym,
hypreal_add_mult_distrib2]
delsimps [hypreal_minus_mult_eq1 RS sym,
hypreal_minus_mult_eq2 RS sym]) 1);
by (res_inst_tac [("y"," inverse(- hypreal_of_real x * hypreal_of_real x)")]
approx_trans 1);
by (rtac inverse_add_Infinitesimal_approx2 1);
by (auto_tac (claset() addSDs [hypreal_of_real_HFinite_diff_Infinitesimal],
simpset() addsimps [hypreal_minus_inverse RS sym,
HFinite_minus_iff]));
by (rtac Infinitesimal_HFinite_mult2 1);
by Auto_tac;
qed "NSDERIV_inverse";
Goal "x \\<noteq> 0 ==> DERIV (%x. inverse(x)) x :> (-(inverse x ^ Suc (Suc 0)))";
by (asm_simp_tac (simpset() addsimps [NSDERIV_inverse,
NSDERIV_DERIV_iff RS sym] delsimps [realpow_Suc]) 1);
qed "DERIV_inverse";
(*--------------------------------------------------------------
Derivative of inverse
-------------------------------------------------------------*)
Goal "[| DERIV f x :> d; f(x) \\<noteq> 0 |] \
\ ==> DERIV (%x. inverse(f x)) x :> (- (d * inverse(f(x) ^ Suc (Suc 0))))";
by (rtac (real_mult_commute RS subst) 1);
by (asm_simp_tac (simpset() addsimps [real_minus_mult_eq1,
realpow_inverse] delsimps [realpow_Suc, real_mult_minus_eq1]) 1);
by (fold_goals_tac [o_def]);
by (blast_tac (claset() addSIs [DERIV_chain,DERIV_inverse]) 1);
qed "DERIV_inverse_fun";
Goal "[| NSDERIV f x :> d; f(x) \\<noteq> 0 |] \
\ ==> NSDERIV (%x. inverse(f x)) x :> (- (d * inverse(f(x) ^ Suc (Suc 0))))";
by (asm_full_simp_tac (simpset() addsimps [NSDERIV_DERIV_iff,
DERIV_inverse_fun] delsimps [realpow_Suc]) 1);
qed "NSDERIV_inverse_fun";
(*--------------------------------------------------------------
Derivative of quotient
-------------------------------------------------------------*)
Goal "[| DERIV f x :> d; DERIV g x :> e; g(x) \\<noteq> 0 |] \
\ ==> DERIV (%y. f(y) / (g y)) x :> (d*g(x) + -(e*f(x))) / (g(x) ^ Suc (Suc 0))";
by (dres_inst_tac [("f","g")] DERIV_inverse_fun 1);
by (dtac DERIV_mult 2);
by (REPEAT(assume_tac 1));
by (asm_full_simp_tac
(simpset() addsimps [real_divide_def, real_add_mult_distrib2,
realpow_inverse,real_minus_mult_eq1] @ real_mult_ac
delsimps [realpow_Suc, real_mult_minus_eq1, real_mult_minus_eq2]) 1);
qed "DERIV_quotient";
Goal "[| NSDERIV f x :> d; DERIV g x :> e; g(x) \\<noteq> 0 |] \
\ ==> NSDERIV (%y. f(y) / (g y)) x :> (d*g(x) \
\ + -(e*f(x))) / (g(x) ^ Suc (Suc 0))";
by (asm_full_simp_tac (simpset() addsimps [NSDERIV_DERIV_iff,
DERIV_quotient] delsimps [realpow_Suc]) 1);
qed "NSDERIV_quotient";
(* ------------------------------------------------------------------------ *)
(* Caratheodory formulation of derivative at a point: standard proof *)
(* ------------------------------------------------------------------------ *)
Goal "(DERIV f x :> l) = \
\ (\\<exists>g. (\\<forall>z. f z - f x = g z * (z - x)) & isCont g x & g x = l)";
by Safe_tac;
by (res_inst_tac
[("x","%z. if z = x then l else (f(z) - f(x)) / (z - x)")] exI 1);
by (auto_tac (claset(),simpset() addsimps [real_mult_assoc,
ARITH_PROVE "z \\<noteq> x ==> z - x \\<noteq> (0::real)"]));
by (auto_tac (claset(),simpset() addsimps [isCont_iff,DERIV_iff]));
by (ALLGOALS(rtac (LIM_equal RS iffD1)));
by (auto_tac (claset(),simpset() addsimps [real_diff_def,real_mult_assoc]));
qed "CARAT_DERIV";
Goal "NSDERIV f x :> l ==> \
\ \\<exists>g. (\\<forall>z. f z - f x = g z * (z - x)) & isNSCont g x & g x = l";
by (auto_tac (claset(),simpset() addsimps [NSDERIV_DERIV_iff,
isNSCont_isCont_iff,CARAT_DERIV]));
qed "CARAT_NSDERIV";
(* How about a NS proof? *)
Goal "(\\<forall>z. f z - f x = g z * (z - x)) & isNSCont g x & g x = l \
\ ==> NSDERIV f x :> l";
by (auto_tac (claset(),
simpset() delsimprocs real_cancel_factor
addsimps [NSDERIV_iff2]));
by (auto_tac (claset(),
simpset() addsimps [hypreal_mult_assoc]));
by (asm_full_simp_tac (simpset() addsimps [hypreal_eq_minus_iff3 RS sym,
hypreal_diff_def]) 1);
by (asm_full_simp_tac (simpset() addsimps [isNSCont_def]) 1);
qed "CARAT_DERIVD";
(*--------------------------------------------------------------------------*)
(* Lemmas about nested intervals and proof by bisection (cf.Harrison) *)
(* All considerably tidied by lcp *)
(*--------------------------------------------------------------------------*)
Goal "(\\<forall>n. (f::nat=>real) n \\<le> f (Suc n)) --> f m \\<le> f(m + no)";
by (induct_tac "no" 1);
by (auto_tac (claset() addIs [order_trans], simpset()));
qed_spec_mp "lemma_f_mono_add";
Goal "[| \\<forall>n. f(n) \\<le> f(Suc n); \
\ \\<forall>n. g(Suc n) \\<le> g(n); \
\ \\<forall>n. f(n) \\<le> g(n) |] \
\ ==> Bseq f";
by (res_inst_tac [("k","f 0"),("K","g 0")] BseqI2 1 THEN rtac allI 1);
by (induct_tac "n" 1);
by (auto_tac (claset() addIs [order_trans], simpset()));
by (res_inst_tac [("y","g(Suc na)")] order_trans 1);
by (induct_tac "na" 2);
by (auto_tac (claset() addIs [order_trans], simpset()));
qed "f_inc_g_dec_Beq_f";
Goal "[| \\<forall>n. f(n) \\<le> f(Suc n); \
\ \\<forall>n. g(Suc n) \\<le> g(n); \
\ \\<forall>n. f(n) \\<le> g(n) |] \
\ ==> Bseq g";
by (stac (Bseq_minus_iff RS sym) 1);
by (res_inst_tac [("g","%x. -(f x)")] f_inc_g_dec_Beq_f 1);
by Auto_tac;
qed "f_inc_g_dec_Beq_g";
Goal "[| \\<forall>n. f n \\<le> f (Suc n); convergent f |] ==> f n \\<le> lim f";
by (rtac real_leI 1);
by (auto_tac (claset(),
simpset() addsimps [convergent_LIMSEQ_iff, LIMSEQ_iff, monoseq_Suc]));
by (dtac real_less_sum_gt_zero 1);
by (dres_inst_tac [("x","f n + - lim f")] spec 1);
by Safe_tac;
by (dres_inst_tac [("P","%na. no\\<le>na --> ?Q na"),("x","no + n")] spec 1);
by Auto_tac;
by (subgoal_tac "lim f \\<le> f(no + n)" 1);
by (induct_tac "no" 2);
by (auto_tac (claset() addIs [order_trans],
simpset() addsimps [real_diff_def, real_abs_def]));
by (dres_inst_tac [("x","f(no + n)"),("no1","no")]
(lemma_f_mono_add RSN (2,order_less_le_trans)) 1);
by (auto_tac (claset(), simpset() addsimps [add_commute]));
qed "f_inc_imp_le_lim";
Goal "convergent g ==> lim (%x. - g x) = - (lim g)";
by (rtac (LIMSEQ_minus RS limI) 1);
by (asm_full_simp_tac (simpset() addsimps [convergent_LIMSEQ_iff]) 1);
qed "lim_uminus";
Goal "[| \\<forall>n. g(Suc n) \\<le> g(n); convergent g |] ==> lim g \\<le> g n";
by (subgoal_tac "- (g n) \\<le> - (lim g)" 1);
by (cut_inst_tac [("f", "%x. - (g x)")] f_inc_imp_le_lim 2);
by (auto_tac (claset(),
simpset() addsimps [lim_uminus, convergent_minus_iff RS sym]));
qed "g_dec_imp_lim_le";
Goal "[| \\<forall>n. f(n) \\<le> f(Suc n); \
\ \\<forall>n. g(Suc n) \\<le> g(n); \
\ \\<forall>n. f(n) \\<le> g(n) |] \
\ ==> \\<exists>l m. l \\<le> m & ((\\<forall>n. f(n) \\<le> l) & f ----> l) & \
\ ((\\<forall>n. m \\<le> g(n)) & g ----> m)";
by (subgoal_tac "monoseq f & monoseq g" 1);
by (force_tac (claset(), simpset() addsimps [LIMSEQ_iff,monoseq_Suc]) 2);
by (subgoal_tac "Bseq f & Bseq g" 1);
by (blast_tac (claset() addIs [f_inc_g_dec_Beq_f, f_inc_g_dec_Beq_g]) 2);
by (auto_tac (claset() addSDs [Bseq_monoseq_convergent],
simpset() addsimps [convergent_LIMSEQ_iff]));
by (res_inst_tac [("x","lim f")] exI 1);
by (res_inst_tac [("x","lim g")] exI 1);
by (auto_tac (claset() addIs [LIMSEQ_le], simpset()));
by (auto_tac (claset(),
simpset() addsimps [f_inc_imp_le_lim, g_dec_imp_lim_le,
convergent_LIMSEQ_iff]));
qed "lemma_nest";
Goal "[| \\<forall>n. f(n) \\<le> f(Suc n); \
\ \\<forall>n. g(Suc n) \\<le> g(n); \
\ \\<forall>n. f(n) \\<le> g(n); \
\ (%n. f(n) - g(n)) ----> 0 |] \
\ ==> \\<exists>l. ((\\<forall>n. f(n) \\<le> l) & f ----> l) & \
\ ((\\<forall>n. l \\<le> g(n)) & g ----> l)";
by (dtac lemma_nest 1 THEN Auto_tac);
by (subgoal_tac "l = m" 1);
by (dres_inst_tac [("X","f")] LIMSEQ_diff 2);
by (auto_tac (claset() addIs [LIMSEQ_unique], simpset()));
qed "lemma_nest_unique";
Goal "a \\<le> b ==> \
\ \\<forall>n. fst (Bolzano_bisect P a b n) \\<le> snd (Bolzano_bisect P a b n)";
by (rtac allI 1);
by (induct_tac "n" 1);
by (auto_tac (claset(), simpset() addsimps [Let_def, split_def]));
qed "Bolzano_bisect_le";
Goal "a \\<le> b ==> \
\ \\<forall>n. fst(Bolzano_bisect P a b n) \\<le> fst (Bolzano_bisect P a b (Suc n))";
by (rtac allI 1);
by (induct_tac "n" 1);
by (auto_tac (claset(),
simpset() addsimps [Bolzano_bisect_le, Let_def, split_def]));
qed "Bolzano_bisect_fst_le_Suc";
Goal "a \\<le> b ==> \
\ \\<forall>n. snd(Bolzano_bisect P a b (Suc n)) \\<le> snd (Bolzano_bisect P a b n)";
by (rtac allI 1);
by (induct_tac "n" 1);
by (auto_tac (claset(),
simpset() addsimps [Bolzano_bisect_le, Let_def, split_def]));
qed "Bolzano_bisect_Suc_le_snd";
Goal "((x::real) = y / (2 * z)) = (2 * x = y/z)";
by Auto_tac;
by (dres_inst_tac [("f","%u. (1/2)*u")] arg_cong 1);
by Auto_tac;
qed "eq_divide_2_times_iff";
Goal "a \\<le> b ==> \
\ snd(Bolzano_bisect P a b n) - fst(Bolzano_bisect P a b n) = \
\ (b-a) / (2 ^ n)";
by (induct_tac "n" 1);
by (auto_tac (claset(),
simpset() addsimps [eq_divide_2_times_iff, real_add_divide_distrib,
Let_def, split_def]));
by (auto_tac (claset(),
simpset() addsimps (real_add_ac@[Bolzano_bisect_le, real_diff_def])));
qed "Bolzano_bisect_diff";
val Bolzano_nest_unique =
[Bolzano_bisect_fst_le_Suc, Bolzano_bisect_Suc_le_snd, Bolzano_bisect_le]
MRS lemma_nest_unique;
(*P_prem is a looping simprule, so it works better if it isn't an assumption*)
val P_prem::notP_prem::rest =
Goal "[| !!a b c. [| P(a,b); P(b,c); a \\<le> b; b \\<le> c|] ==> P(a,c); \
\ ~ P(a,b); a \\<le> b |] ==> \
\ ~ P(fst(Bolzano_bisect P a b n), snd(Bolzano_bisect P a b n))";
by (cut_facts_tac rest 1);
by (induct_tac "n" 1);
by (auto_tac (claset(),
simpset() delsimps [surjective_pairing RS sym]
addsimps [notP_prem, Let_def, split_def]));
by (swap_res_tac [P_prem] 1);
by (assume_tac 1);
by (auto_tac (claset(), simpset() addsimps [Bolzano_bisect_le]));
qed "not_P_Bolzano_bisect";
(*Now we re-package P_prem as a formula*)
Goal "[| \\<forall>a b c. P(a,b) & P(b,c) & a \\<le> b & b \\<le> c --> P(a,c); \
\ ~ P(a,b); a \\<le> b |] ==> \
\ \\<forall>n. ~ P(fst(Bolzano_bisect P a b n), snd(Bolzano_bisect P a b n))";
by (blast_tac (claset() addSEs [not_P_Bolzano_bisect RSN (2,rev_notE)]) 1);
qed "not_P_Bolzano_bisect'";
Goal "[| \\<forall>a b c. P(a,b) & P(b,c) & a \\<le> b & b \\<le> c --> P(a,c); \
\ \\<forall>x. \\<exists>d::real. 0 < d & \
\ (\\<forall>a b. a \\<le> x & x \\<le> b & (b - a) < d --> P(a,b)); \
\ a \\<le> b |] \
\ ==> P(a,b)";
by (rtac (inst "P1" "P" Bolzano_nest_unique RS exE) 1);
by (REPEAT (assume_tac 1));
by (rtac LIMSEQ_minus_cancel 1);
by (asm_simp_tac (simpset() addsimps [Bolzano_bisect_diff,
LIMSEQ_divide_realpow_zero]) 1);
by (rtac ccontr 1);
by (dtac not_P_Bolzano_bisect' 1);
by (REPEAT (assume_tac 1));
by (rename_tac "l" 1);
by (dres_inst_tac [("x","l")] spec 1 THEN Clarify_tac 1);
by (rewtac LIMSEQ_def);
by (dres_inst_tac [("P", "%r. 0<r --> ?Q r"), ("x","d/2")] spec 1);
by (dres_inst_tac [("P", "%r. 0<r --> ?Q r"), ("x","d/2")] spec 1);
by (dtac real_less_half_sum 1);
by Safe_tac;
(*linear arithmetic bug if we just use Asm_simp_tac*)
by (ALLGOALS Asm_full_simp_tac);
by (dres_inst_tac [("x","fst(Bolzano_bisect P a b (no + noa))")] spec 1);
by (dres_inst_tac [("x","snd(Bolzano_bisect P a b (no + noa))")] spec 1);
by Safe_tac;
by (ALLGOALS Asm_simp_tac);
by (res_inst_tac [("y","abs(fst(Bolzano_bisect P a b(no + noa)) - l) + \
\ abs(snd(Bolzano_bisect P a b(no + noa)) - l)")]
order_le_less_trans 1);
by (asm_simp_tac (simpset() addsimps [real_abs_def]) 1);
by (rtac (real_sum_of_halves RS subst) 1);
by (rtac real_add_less_mono 1);
by (ALLGOALS
(asm_full_simp_tac (simpset() addsimps [symmetric real_diff_def])));
qed "lemma_BOLZANO";
Goal "((\\<forall>a b c. (a \\<le> b & b \\<le> c & P(a,b) & P(b,c)) --> P(a,c)) & \
\ (\\<forall>x. \\<exists>d::real. 0 < d & \
\ (\\<forall>a b. a \\<le> x & x \\<le> b & (b - a) < d --> P(a,b)))) \
\ --> (\\<forall>a b. a \\<le> b --> P(a,b))";
by (Clarify_tac 1);
by (blast_tac (claset() addIs [lemma_BOLZANO]) 1);
qed "lemma_BOLZANO2";
(*----------------------------------------------------------------------------*)
(* Intermediate Value Theorem (prove contrapositive by bisection) *)
(*----------------------------------------------------------------------------*)
Goal "[| f(a) \\<le> y & y \\<le> f(b); \
\ a \\<le> b; \
\ (\\<forall>x. a \\<le> x & x \\<le> b --> isCont f x) |] \
\ ==> \\<exists>x. a \\<le> x & x \\<le> b & f(x) = y";
by (rtac contrapos_pp 1);
by (assume_tac 1);
by (cut_inst_tac
[("P","%(u,v). a \\<le> u & u \\<le> v & v \\<le> b --> ~(f(u) \\<le> y & y \\<le> f(v))")]
lemma_BOLZANO2 1);
by Safe_tac;
by (ALLGOALS(Asm_full_simp_tac));
by (asm_full_simp_tac (simpset() addsimps [isCont_iff,LIM_def]) 1);
by (rtac ccontr 1);
by (subgoal_tac "a \\<le> x & x \\<le> b" 1);
by (Asm_full_simp_tac 2);
by (dres_inst_tac [("P", "%d. 0<d --> ?P d"),("x","1")] spec 2);
by (Step_tac 2);
by (Asm_full_simp_tac 2);
by (Asm_full_simp_tac 2);
by (REPEAT(blast_tac (claset() addIs [order_trans]) 2));
by (REPEAT(dres_inst_tac [("x","x")] spec 1));
by (Asm_full_simp_tac 1);
by (dres_inst_tac [("P", "%r. ?P r --> (\\<exists>s. 0<s & ?Q r s)"),
("x","abs(y - f x)")] spec 1);
by Safe_tac;
by (asm_full_simp_tac (simpset() addsimps []) 1);
by (dres_inst_tac [("x","s")] spec 1);
by (Clarify_tac 1);
by (cut_inst_tac [("x","f x"),("y","y")] linorder_less_linear 1);
by Safe_tac;
by (dres_inst_tac [("x","ba - x")] spec 1);
by (ALLGOALS (asm_full_simp_tac (simpset() addsimps [thm"abs_if"])));
by (dres_inst_tac [("x","aa - x")] spec 1);
by (case_tac "x \\<le> aa" 1);
by (ALLGOALS Asm_full_simp_tac);
by (dres_inst_tac [("z","x"),("w","aa")] real_le_anti_sym 1);
by (assume_tac 1 THEN Asm_full_simp_tac 1);
qed "IVT";
Goal "[| f(b) \\<le> y & y \\<le> f(a); \
\ a \\<le> b; \
\ (\\<forall>x. a \\<le> x & x \\<le> b --> isCont f x) \
\ |] ==> \\<exists>x. a \\<le> x & x \\<le> b & f(x) = y";
by (subgoal_tac "- f a \\<le> -y & -y \\<le> - f b" 1);
by (thin_tac "f b \\<le> y & y \\<le> f a" 1);
by (dres_inst_tac [("f","%x. - f x")] IVT 1);
by (auto_tac (claset() addIs [isCont_minus],simpset()));
qed "IVT2";
(*HOL style here: object-level formulations*)
Goal "(f(a) \\<le> y & y \\<le> f(b) & a \\<le> b & \
\ (\\<forall>x. a \\<le> x & x \\<le> b --> isCont f x)) \
\ --> (\\<exists>x. a \\<le> x & x \\<le> b & f(x) = y)";
by (blast_tac (claset() addIs [IVT]) 1);
qed "IVT_objl";
Goal "(f(b) \\<le> y & y \\<le> f(a) & a \\<le> b & \
\ (\\<forall>x. a \\<le> x & x \\<le> b --> isCont f x)) \
\ --> (\\<exists>x. a \\<le> x & x \\<le> b & f(x) = y)";
by (blast_tac (claset() addIs [IVT2]) 1);
qed "IVT2_objl";
(*---------------------------------------------------------------------------*)
(* By bisection, function continuous on closed interval is bounded above *)
(*---------------------------------------------------------------------------*)
Goal "abs (real x) = real (x::nat)";
by (auto_tac (claset() addIs [abs_eqI1], simpset()));
qed "abs_real_of_nat_cancel";
Addsimps [abs_real_of_nat_cancel];
Goal "~ abs(x) + (1::real) < x";
by (rtac real_leD 1);
by (auto_tac (claset() addIs [abs_ge_self RS order_trans],simpset()));
qed "abs_add_one_not_less_self";
Addsimps [abs_add_one_not_less_self];
Goal "[| a \\<le> b; \\<forall>x. a \\<le> x & x \\<le> b --> isCont f x |]\
\ ==> \\<exists>M. \\<forall>x. a \\<le> x & x \\<le> b --> f(x) \\<le> M";
by (cut_inst_tac [("P","%(u,v). a \\<le> u & u \\<le> v & v \\<le> b --> \
\ (\\<exists>M. \\<forall>x. u \\<le> x & x \\<le> v --> f x \\<le> M)")]
lemma_BOLZANO2 1);
by Safe_tac;
by (ALLGOALS Asm_full_simp_tac);
by (rename_tac "x xa ya M Ma" 1);
by (cut_inst_tac [("x","M"),("y","Ma")] linorder_linear 1);
by Safe_tac;
by (res_inst_tac [("x","Ma")] exI 1);
by (Clarify_tac 1);
by (cut_inst_tac [("x","xb"),("y","xa")] linorder_linear 1);
by (Force_tac 1);
by (res_inst_tac [("x","M")] exI 1);
by (Clarify_tac 1);
by (cut_inst_tac [("x","xb"),("y","xa")] linorder_linear 1);
by (Force_tac 1);
by (case_tac "a \\<le> x & x \\<le> b" 1);
by (res_inst_tac [("x","1")] exI 2);
by (Force_tac 2);
by (asm_full_simp_tac (simpset() addsimps [LIM_def,isCont_iff]) 1);
by (dres_inst_tac [("x","x")] spec 1 THEN Auto_tac);
by (thin_tac "\\<forall>M. \\<exists>x. a \\<le> x & x \\<le> b & ~ f x \\<le> M" 1);
by (dres_inst_tac [("x","1")] spec 1);
by Auto_tac;
by (res_inst_tac [("x","s")] exI 1 THEN Clarify_tac 1);
by (res_inst_tac [("x","abs(f x) + 1")] exI 1 THEN Clarify_tac 1);
by (dres_inst_tac [("x","xa - x")] spec 1 THEN Safe_tac);
by (arith_tac 1);
by (arith_tac 1);
by (asm_full_simp_tac (simpset() addsimps [abs_ge_self]) 1);
by (arith_tac 1);
qed "isCont_bounded";
(*----------------------------------------------------------------------------*)
(* Refine the above to existence of least upper bound *)
(*----------------------------------------------------------------------------*)
Goal "((\\<exists>x. x \\<in> S) & (\\<exists>y. isUb UNIV S (y::real))) --> \
\ (\\<exists>t. isLub UNIV S t)";
by (blast_tac (claset() addIs [reals_complete]) 1);
qed "lemma_reals_complete";
Goal "[| a \\<le> b; \\<forall>x. a \\<le> x & x \\<le> b --> isCont f x |] \
\ ==> \\<exists>M. (\\<forall>x. a \\<le> x & x \\<le> b --> f(x) \\<le> M) & \
\ (\\<forall>N. N < M --> (\\<exists>x. a \\<le> x & x \\<le> b & N < f(x)))";
by (cut_inst_tac [("S","Collect (%y. \\<exists>x. a \\<le> x & x \\<le> b & y = f x)")]
lemma_reals_complete 1);
by Auto_tac;
by (dtac isCont_bounded 1 THEN assume_tac 1);
by (auto_tac (claset(),simpset() addsimps [isUb_def,leastP_def,
isLub_def,setge_def,setle_def]));
by (rtac exI 1 THEN Auto_tac);
by (REPEAT(dtac spec 1) THEN Auto_tac);
by (dres_inst_tac [("x","x")] spec 1);
by (auto_tac (claset() addSIs [real_leI],simpset()));
qed "isCont_has_Ub";
(*----------------------------------------------------------------------------*)
(* Now show that it attains its upper bound *)
(*----------------------------------------------------------------------------*)
Goal "[| a \\<le> b; \\<forall>x. a \\<le> x & x \\<le> b --> isCont f x |] \
\ ==> \\<exists>M. (\\<forall>x. a \\<le> x & x \\<le> b --> f(x) \\<le> M) & \
\ (\\<exists>x. a \\<le> x & x \\<le> b & f(x) = M)";
by (ftac isCont_has_Ub 1 THEN assume_tac 1);
by (Clarify_tac 1);
by (res_inst_tac [("x","M")] exI 1);
by (Asm_full_simp_tac 1);
by (rtac ccontr 1);
by (subgoal_tac "\\<forall>x. a \\<le> x & x \\<le> b --> f x < M" 1 THEN Step_tac 1);
by (rtac ccontr 2 THEN dtac real_leI 2);
by (dres_inst_tac [("z","M")] real_le_anti_sym 2);
by (REPEAT(Blast_tac 2));
by (subgoal_tac "\\<forall>x. a \\<le> x & x \\<le> b --> isCont (%x. inverse(M - f x)) x" 1);
by Safe_tac;
by (EVERY[rtac isCont_inverse 2, rtac isCont_diff 2, rtac notI 4]);
by (ALLGOALS(asm_full_simp_tac (simpset() addsimps [diff_eq_eq])));
by (Blast_tac 2);
by (subgoal_tac
"\\<exists>k. \\<forall>x. a \\<le> x & x \\<le> b --> (%x. inverse(M - (f x))) x \\<le> k" 1);
by (rtac isCont_bounded 2);
by Safe_tac;
by (subgoal_tac "\\<forall>x. a \\<le> x & x \\<le> b --> 0 < inverse(M - f(x))" 1);
by (Asm_full_simp_tac 1);
by Safe_tac;
by (asm_full_simp_tac (simpset() addsimps [less_diff_eq]) 2);
by (subgoal_tac
"\\<forall>x. a \\<le> x & x \\<le> b --> (%x. inverse(M - (f x))) x < (k + 1)" 1);
by Safe_tac;
by (res_inst_tac [("y","k")] order_le_less_trans 2);
by (asm_full_simp_tac (simpset() addsimps [real_zero_less_one]) 3);
by (Asm_full_simp_tac 2);
by (subgoal_tac "\\<forall>x. a \\<le> x & x \\<le> b --> \
\ inverse(k + 1) < inverse((%x. inverse(M - (f x))) x)" 1);
by Safe_tac;
by (rtac real_inverse_less_swap 2);
by (ALLGOALS Asm_full_simp_tac);
by (dres_inst_tac [("P", "%N. N<M --> ?Q N"),
("x","M - inverse(k + 1)")] spec 1);
by (Step_tac 1 THEN dtac real_leI 1);
by (dtac (le_diff_eq RS iffD1) 1);
by (REPEAT(dres_inst_tac [("x","a")] spec 1));
by (Asm_full_simp_tac 1);
by (asm_full_simp_tac
(simpset() addsimps [real_inverse_eq_divide, pos_real_divide_le_eq]) 1);
by (cut_inst_tac [("x","k"),("y","M-f a")] real_0_less_mult_iff 1);
by (Asm_full_simp_tac 1);
(*last one*)
by (REPEAT(dres_inst_tac [("x","x")] spec 1));
by (Asm_full_simp_tac 1);
qed "isCont_eq_Ub";
(*----------------------------------------------------------------------------*)
(* Same theorem for lower bound *)
(*----------------------------------------------------------------------------*)
Goal "[| a \\<le> b; \\<forall>x. a \\<le> x & x \\<le> b --> isCont f x |] \
\ ==> \\<exists>M. (\\<forall>x. a \\<le> x & x \\<le> b --> M \\<le> f(x)) & \
\ (\\<exists>x. a \\<le> x & x \\<le> b & f(x) = M)";
by (subgoal_tac "\\<forall>x. a \\<le> x & x \\<le> b --> isCont (%x. -(f x)) x" 1);
by (blast_tac (claset() addIs [isCont_minus]) 2);
by (dres_inst_tac [("f","(%x. -(f x))")] isCont_eq_Ub 1);
by Safe_tac;
by Auto_tac;
qed "isCont_eq_Lb";
(* ------------------------------------------------------------------------- *)
(* Another version. *)
(* ------------------------------------------------------------------------- *)
Goal "[|a \\<le> b; \\<forall>x. a \\<le> x & x \\<le> b --> isCont f x |] \
\ ==> \\<exists>L M. (\\<forall>x. a \\<le> x & x \\<le> b --> L \\<le> f(x) & f(x) \\<le> M) & \
\ (\\<forall>y. L \\<le> y & y \\<le> M --> (\\<exists>x. a \\<le> x & x \\<le> b & (f(x) = y)))";
by (ftac isCont_eq_Lb 1);
by (ftac isCont_eq_Ub 2);
by (REPEAT(assume_tac 1));
by Safe_tac;
by (res_inst_tac [("x","f x")] exI 1);
by (res_inst_tac [("x","f xa")] exI 1);
by (Asm_full_simp_tac 1);
by Safe_tac;
by (cut_inst_tac [("x","x"),("y","xa")] linorder_linear 1);
by Safe_tac;
by (cut_inst_tac [("f","f"),("a","x"),("b","xa"),("y","y")] IVT_objl 1);
by (cut_inst_tac [("f","f"),("a","xa"),("b","x"),("y","y")] IVT2_objl 2);
by Safe_tac;
by (res_inst_tac [("x","xb")] exI 2);
by (res_inst_tac [("x","xb")] exI 4);
by (ALLGOALS(Asm_full_simp_tac));
qed "isCont_Lb_Ub";
(*----------------------------------------------------------------------------*)
(* If f'(x) > 0 then x is locally strictly increasing at the right *)
(*----------------------------------------------------------------------------*)
Goalw [deriv_def,LIM_def]
"[| DERIV f x :> l; 0 < l |] \
\ ==> \\<exists>d. 0 < d & (\\<forall>h. 0 < h & h < d --> f(x) < f(x + h))";
by (dtac spec 1 THEN Auto_tac);
by (res_inst_tac [("x","s")] exI 1 THEN Auto_tac);
by (subgoal_tac "0 < l*h" 1);
by (asm_full_simp_tac (simpset() addsimps [real_0_less_mult_iff]) 2);
by (dres_inst_tac [("x","h")] spec 1);
by (asm_full_simp_tac
(simpset() addsimps [real_abs_def, real_inverse_eq_divide,
pos_real_le_divide_eq, pos_real_less_divide_eq]
addsplits [split_if_asm]) 1);
qed "DERIV_left_inc";
Goalw [deriv_def,LIM_def]
"[| DERIV f x :> l; l < 0 |] ==> \
\ \\<exists>d. 0 < d & (\\<forall>h. 0 < h & h < d --> f(x) < f(x - h))";
by (dres_inst_tac [("x","-l")] spec 1 THEN Auto_tac);
by (res_inst_tac [("x","s")] exI 1 THEN Auto_tac);
by (subgoal_tac "l*h < 0" 1);
by (asm_full_simp_tac (simpset() addsimps [real_mult_less_0_iff]) 2);
by (dres_inst_tac [("x","-h")] spec 1);
by (asm_full_simp_tac
(simpset() addsimps [real_abs_def, real_inverse_eq_divide,
pos_real_less_divide_eq,
symmetric real_diff_def]
addsplits [split_if_asm]
delsimprocs [fast_real_arith_simproc]) 1);
by (subgoal_tac "0 < (f (x - h) - f x)/h" 1);
by (arith_tac 2);
by (asm_full_simp_tac
(simpset() addsimps [pos_real_less_divide_eq]) 1);
qed "DERIV_left_dec";
Goal "[| DERIV f x :> l; \
\ \\<exists>d. 0 < d & (\\<forall>y. abs(x - y) < d --> f(y) \\<le> f(x)) |] \
\ ==> l = 0";
by (res_inst_tac [("R1.0","l"),("R2.0","0")] real_linear_less2 1);
by Safe_tac;
by (dtac DERIV_left_dec 1);
by (dtac DERIV_left_inc 3);
by Safe_tac;
by (dres_inst_tac [("d1.0","d"),("d2.0","da")] real_lbound_gt_zero 1);
by (dres_inst_tac [("d1.0","d"),("d2.0","da")] real_lbound_gt_zero 3);
by Safe_tac;
by (dres_inst_tac [("x","x - e")] spec 1);
by (dres_inst_tac [("x","x + e")] spec 2);
by (auto_tac (claset(), simpset() addsimps [real_abs_def]));
qed "DERIV_local_max";
(*----------------------------------------------------------------------------*)
(* Similar theorem for a local minimum *)
(*----------------------------------------------------------------------------*)
Goal "[| DERIV f x :> l; \
\ \\<exists>d::real. 0 < d & (\\<forall>y. abs(x - y) < d --> f(x) \\<le> f(y)) |] \
\ ==> l = 0";
by (dtac (DERIV_minus RS DERIV_local_max) 1);
by Auto_tac;
qed "DERIV_local_min";
(*----------------------------------------------------------------------------*)
(* In particular if a function is locally flat *)
(*----------------------------------------------------------------------------*)
Goal "[| DERIV f x :> l; \
\ \\<exists>d. 0 < d & (\\<forall>y. abs(x - y) < d --> f(x) = f(y)) |] \
\ ==> l = 0";
by (auto_tac (claset() addSDs [DERIV_local_max],simpset()));
qed "DERIV_local_const";
(*----------------------------------------------------------------------------*)
(* Lemma about introducing open ball in open interval *)
(*----------------------------------------------------------------------------*)
Goal "[| a < x; x < b |] ==> \
\ \\<exists>d::real. 0 < d & (\\<forall>y. abs(x - y) < d --> a < y & y < b)";
by (simp_tac (simpset() addsimps [abs_interval_iff]) 1);
by (cut_inst_tac [("x","x - a"),("y","b - x")] linorder_linear 1);
by Safe_tac;
by (res_inst_tac [("x","x - a")] exI 1);
by (res_inst_tac [("x","b - x")] exI 2);
by Auto_tac;
by (auto_tac (claset(),simpset() addsimps [less_diff_eq]));
qed "lemma_interval_lt";
Goal "[| a < x; x < b |] ==> \
\ \\<exists>d::real. 0 < d & (\\<forall>y. abs(x - y) < d --> a \\<le> y & y \\<le> b)";
by (dtac lemma_interval_lt 1);
by Auto_tac;
by (auto_tac (claset() addSIs [exI] ,simpset()));
qed "lemma_interval";
(*-----------------------------------------------------------------------
Rolle's Theorem
If f is defined and continuous on the finite closed interval [a,b]
and differentiable a least on the open interval (a,b), and f(a) = f(b),
then x0 \\<in> (a,b) such that f'(x0) = 0
----------------------------------------------------------------------*)
Goal "[| a < b; f(a) = f(b); \
\ \\<forall>x. a \\<le> x & x \\<le> b --> isCont f x; \
\ \\<forall>x. a < x & x < b --> f differentiable x \
\ |] ==> \\<exists>z. a < z & z < b & DERIV f z :> 0";
by (ftac (order_less_imp_le RS isCont_eq_Ub) 1);
by (EVERY1[assume_tac,Step_tac]);
by (ftac (order_less_imp_le RS isCont_eq_Lb) 1);
by (EVERY1[assume_tac,Step_tac]);
by (case_tac "a < x & x < b" 1 THEN etac conjE 1);
by (Asm_full_simp_tac 2);
by (forw_inst_tac [("a","a"),("x","x")] lemma_interval 1);
by (EVERY1[assume_tac,etac exE]);
by (res_inst_tac [("x","x")] exI 1 THEN Asm_full_simp_tac 1);
by (subgoal_tac "(\\<exists>l. DERIV f x :> l) & \
\ (\\<exists>d. 0 < d & (\\<forall>y. abs(x - y) < d --> f(y) \\<le> f(x)))" 1);
by (Clarify_tac 1 THEN rtac conjI 2);
by (blast_tac (claset() addIs [differentiableD]) 2);
by (Blast_tac 2);
by (ftac DERIV_local_max 1);
by (EVERY1[Blast_tac,Blast_tac]);
by (case_tac "a < xa & xa < b" 1 THEN etac conjE 1);
by (Asm_full_simp_tac 2);
by (forw_inst_tac [("a","a"),("x","xa")] lemma_interval 1);
by (EVERY1[assume_tac,etac exE]);
by (res_inst_tac [("x","xa")] exI 1 THEN Asm_full_simp_tac 1);
by (subgoal_tac "(\\<exists>l. DERIV f xa :> l) & \
\ (\\<exists>d. 0 < d & (\\<forall>y. abs(xa - y) < d --> f(xa) \\<le> f(y)))" 1);
by (Clarify_tac 1 THEN rtac conjI 2);
by (blast_tac (claset() addIs [differentiableD]) 2);
by (Blast_tac 2);
by (ftac DERIV_local_min 1);
by (EVERY1[Blast_tac,Blast_tac]);
by (subgoal_tac "\\<forall>x. a \\<le> x & x \\<le> b --> f(x) = f(b)" 1);
by (Clarify_tac 2);
by (rtac real_le_anti_sym 2);
by (subgoal_tac "f b = f x" 2);
by (Asm_full_simp_tac 2);
by (res_inst_tac [("x1","a"),("y1","x")] (order_le_imp_less_or_eq RS disjE) 2);
by (assume_tac 2);
by (dres_inst_tac [("z","x"),("w","b")] real_le_anti_sym 2);
by (subgoal_tac "f b = f xa" 5);
by (Asm_full_simp_tac 5);
by (res_inst_tac [("x1","a"),("y1","xa")] (order_le_imp_less_or_eq RS disjE) 5);
by (assume_tac 5);
by (dres_inst_tac [("z","xa"),("w","b")] real_le_anti_sym 5);
by (REPEAT(Asm_full_simp_tac 2));
by (dtac real_dense 1 THEN etac exE 1);
by (res_inst_tac [("x","r")] exI 1 THEN Asm_simp_tac 1);
by (etac conjE 1);
by (forw_inst_tac [("a","a"),("x","r")] lemma_interval 1);
by (EVERY1[assume_tac, etac exE]);
by (subgoal_tac "(\\<exists>l. DERIV f r :> l) & \
\ (\\<exists>d. 0 < d & (\\<forall>y. abs(r - y) < d --> f(r) = f(y)))" 1);
by (Clarify_tac 1 THEN rtac conjI 2);
by (blast_tac (claset() addIs [differentiableD]) 2);
by (EVERY1[ftac DERIV_local_const, Blast_tac, Blast_tac]);
by (res_inst_tac [("x","d")] exI 1);
by (EVERY1[rtac conjI, Blast_tac, rtac allI, rtac impI]);
by (res_inst_tac [("s","f b")] trans 1);
by (blast_tac (claset() addSDs [order_less_imp_le]) 1);
by (rtac sym 1 THEN Blast_tac 1);
qed "Rolle";
(*----------------------------------------------------------------------------*)
(* Mean value theorem *)
(*----------------------------------------------------------------------------*)
Goal "f a - (f b - f a)/(b - a) * a = \
\ f b - (f b - f a)/(b - a) * (b::real)";
by (case_tac "a = b" 1);
by (asm_full_simp_tac (simpset() addsimps [DIVISION_BY_ZERO]) 1);
by (res_inst_tac [("c1","b - a")] (real_mult_left_cancel RS iffD1) 1);
by (arith_tac 1);
by (auto_tac (claset(),
simpset() addsimps [real_diff_mult_distrib2]));
by (auto_tac (claset(),
simpset() addsimps [real_diff_mult_distrib]));
qed "lemma_MVT";
Goal "[| a < b; \
\ \\<forall>x. a \\<le> x & x \\<le> b --> isCont f x; \
\ \\<forall>x. a < x & x < b --> f differentiable x |] \
\ ==> \\<exists>l z. a < z & z < b & DERIV f z :> l & \
\ (f(b) - f(a) = (b - a) * l)";
by (dres_inst_tac [("f","%x. f(x) - (((f(b) - f(a)) / (b - a)) * x)")]
Rolle 1);
by (rtac lemma_MVT 1);
by Safe_tac;
by (rtac isCont_diff 1 THEN Blast_tac 1);
by (rtac (isCont_const RS isCont_mult) 1);
by (rtac isCont_Id 1);
by (dres_inst_tac [("P", "%x. ?Pre x --> f differentiable x"),
("x","x")] spec 1);
by (asm_full_simp_tac (simpset() addsimps [differentiable_def]) 1);
by Safe_tac;
by (res_inst_tac [("x","xa - ((f(b) - f(a)) / (b - a))")] exI 1);
by (rtac DERIV_diff 1 THEN assume_tac 1);
(*derivative of a linear function is the constant...*)
by (subgoal_tac "(%x. (f b - f a) * x / (b - a)) = \
\ op * ((f b - f a) / (b - a))" 1);
by (rtac ext 2 THEN Simp_tac 2);
by (Asm_full_simp_tac 1);
(*final case*)
by (res_inst_tac [("x","((f(b) - f(a)) / (b - a))")] exI 1);
by (res_inst_tac [("x","z")] exI 1);
by Safe_tac;
by (Asm_full_simp_tac 2);
by (subgoal_tac "DERIV (%x. ((f(b) - f(a)) / (b - a)) * x) z :> \
\ ((f(b) - f(a)) / (b - a))" 1);
by (rtac DERIV_cmult_Id 2);
by (dtac DERIV_add 1 THEN assume_tac 1);
by (asm_full_simp_tac (simpset() addsimps [real_add_assoc, real_diff_def]) 1);
qed "MVT";
(*----------------------------------------------------------------------------*)
(* Theorem that function is constant if its derivative is 0 over an interval. *)
(*----------------------------------------------------------------------------*)
Goal "[| a < b; \
\ \\<forall>x. a \\<le> x & x \\<le> b --> isCont f x; \
\ \\<forall>x. a < x & x < b --> DERIV f x :> 0 |] \
\ ==> (f b = f a)";
by (dtac MVT 1 THEN assume_tac 1);
by (blast_tac (claset() addIs [differentiableI]) 1);
by (auto_tac (claset() addSDs [DERIV_unique],simpset()
addsimps [diff_eq_eq]));
qed "DERIV_isconst_end";
Goal "[| a < b; \
\ \\<forall>x. a \\<le> x & x \\<le> b --> isCont f x; \
\ \\<forall>x. a < x & x < b --> DERIV f x :> 0 |] \
\ ==> \\<forall>x. a \\<le> x & x \\<le> b --> f x = f a";
by Safe_tac;
by (dres_inst_tac [("x","a")] order_le_imp_less_or_eq 1);
by Safe_tac;
by (dres_inst_tac [("b","x")] DERIV_isconst_end 1);
by Auto_tac;
qed "DERIV_isconst1";
Goal "[| a < b; \
\ \\<forall>x. a \\<le> x & x \\<le> b --> isCont f x; \
\ \\<forall>x. a < x & x < b --> DERIV f x :> 0; \
\ a \\<le> x; x \\<le> b |] \
\ ==> f x = f a";
by (blast_tac (claset() addDs [DERIV_isconst1]) 1);
qed "DERIV_isconst2";
Goal "\\<forall>x. DERIV f x :> 0 ==> f(x) = f(y)";
by (res_inst_tac [("R1.0","x"),("R2.0","y")] real_linear_less2 1);
by (rtac sym 1);
by (auto_tac (claset() addIs [DERIV_isCont,DERIV_isconst_end],simpset()));
qed "DERIV_isconst_all";
Goal "[|a \\<noteq> b; \\<forall>x. DERIV f x :> k |] ==> (f(b) - f(a)) = (b - a) * k";
by (res_inst_tac [("R1.0","a"),("R2.0","b")] real_linear_less2 1);
by Auto_tac;
by (ALLGOALS(dres_inst_tac [("f","f")] MVT));
by (auto_tac (claset() addDs [DERIV_isCont,DERIV_unique],simpset() addsimps
[differentiable_def]));
by (auto_tac (claset() addDs [DERIV_unique],
simpset() addsimps [real_add_mult_distrib, real_diff_def]));
qed "DERIV_const_ratio_const";
Goal "[|a \\<noteq> b; \\<forall>x. DERIV f x :> k |] ==> (f(b) - f(a))/(b - a) = k";
by (res_inst_tac [("c1","b - a")] (real_mult_right_cancel RS iffD1) 1);
by (auto_tac (claset() addSDs [DERIV_const_ratio_const],
simpset() addsimps [real_mult_assoc]));
qed "DERIV_const_ratio_const2";
Goal "((a + b) /2 - a) = (b - a)/(2::real)";
by Auto_tac;
qed "real_average_minus_first";
Addsimps [real_average_minus_first];
Goal "((b + a)/2 - a) = (b - a)/(2::real)";
by Auto_tac;
qed "real_average_minus_second";
Addsimps [real_average_minus_second];
(* Gallileo's "trick": average velocity = av. of end velocities *)
Goal "[|a \\<noteq> (b::real); \\<forall>x. DERIV v x :> k|] \
\ ==> v((a + b)/2) = (v a + v b)/2";
by (res_inst_tac [("R1.0","a"),("R2.0","b")] real_linear_less2 1);
by Safe_tac;
by (ftac DERIV_const_ratio_const2 1 THEN assume_tac 1);
by (ftac DERIV_const_ratio_const2 2 THEN assume_tac 2);
by (dtac real_less_half_sum 1);
by (dtac real_gt_half_sum 2);
by (ftac (real_not_refl2 RS DERIV_const_ratio_const2) 1 THEN assume_tac 1);
by (dtac ((real_not_refl2 RS not_sym) RS DERIV_const_ratio_const2) 2
THEN assume_tac 2);
by (ALLGOALS (dres_inst_tac [("f","%u. (b-a)*u")] arg_cong));
by (auto_tac (claset(), simpset() addsimps [real_inverse_eq_divide]));
by (asm_full_simp_tac (simpset() addsimps [real_add_commute, eq_commute]) 1);
qed "DERIV_const_average";
(* ------------------------------------------------------------------------ *)
(* Dull lemma that an continuous injection on an interval must have a strict*)
(* maximum at an end point, not in the middle. *)
(* ------------------------------------------------------------------------ *)
Goal "[|0 < d; \\<forall>z. abs(z - x) \\<le> d --> g(f z) = z; \
\ \\<forall>z. abs(z - x) \\<le> d --> isCont f z |] \
\ ==> ~(\\<forall>z. abs(z - x) \\<le> d --> f(z) \\<le> f(x))";
by (rtac notI 1);
by (rotate_tac 3 1);
by (forw_inst_tac [("x","x - d")] spec 1);
by (forw_inst_tac [("x","x + d")] spec 1);
by Safe_tac;
by (cut_inst_tac [("x","f(x - d)"),("y","f(x + d)")]
(ARITH_PROVE "x \\<le> y | y \\<le> (x::real)") 4);
by (etac disjE 4);
by (REPEAT(arith_tac 1));
by (cut_inst_tac [("f","f"),("a","x - d"),("b","x"),("y","f(x + d)")]
IVT_objl 1);
by Safe_tac;
by (arith_tac 1);
by (asm_full_simp_tac (simpset() addsimps [abs_le_interval_iff]) 1);
by (dres_inst_tac [("f","g")] arg_cong 1);
by (rotate_tac 2 1);
by (forw_inst_tac [("x","xa")] spec 1);
by (dres_inst_tac [("x","x + d")] spec 1);
by (asm_full_simp_tac (simpset() addsimps [abs_le_interval_iff]) 1);
(* 2nd case: similar *)
by (cut_inst_tac [("f","f"),("a","x"),("b","x + d"),("y","f(x - d)")]
IVT2_objl 1);
by Safe_tac;
by (arith_tac 1);
by (asm_full_simp_tac (simpset() addsimps [abs_le_interval_iff]) 1);
by (dres_inst_tac [("f","g")] arg_cong 1);
by (rotate_tac 2 1);
by (forw_inst_tac [("x","xa")] spec 1);
by (dres_inst_tac [("x","x - d")] spec 1);
by (asm_full_simp_tac (simpset() addsimps [abs_le_interval_iff]) 1);
qed "lemma_isCont_inj";
(* ------------------------------------------------------------------------ *)
(* Similar version for lower bound *)
(* ------------------------------------------------------------------------ *)
Goal "[|0 < d; \\<forall>z. abs(z - x) \\<le> d --> g(f z) = z; \
\ \\<forall>z. abs(z - x) \\<le> d --> isCont f z |] \
\ ==> ~(\\<forall>z. abs(z - x) \\<le> d --> f(x) \\<le> f(z))";
by (auto_tac (claset() addSDs [(asm_full_simplify (simpset())
(read_instantiate [("f","%x. - f x"),("g","%y. g(-y)"),("x","x"),("d","d")]
lemma_isCont_inj))],simpset() addsimps [isCont_minus]));
qed "lemma_isCont_inj2";
(* ------------------------------------------------------------------------ *)
(* Show there's an interval surrounding f(x) in f[[x - d, x + d]] *)
(* Also from John's theory *)
(* ------------------------------------------------------------------------ *)
val lemma_le = ARITH_PROVE "0 \\<le> (d::real) ==> -d \\<le> d";
(* FIXME: awful proof - needs improvement *)
Goal "[| 0 < d; \\<forall>z. abs(z - x) \\<le> d --> g(f z) = z; \
\ \\<forall>z. abs(z - x) \\<le> d --> isCont f z |] \
\ ==> \\<exists>e. 0 < e & \
\ (\\<forall>y. \
\ abs(y - f(x)) \\<le> e --> \
\ (\\<exists>z. abs(z - x) \\<le> d & (f z = y)))";
by (ftac order_less_imp_le 1);
by (dtac (lemma_le RS (asm_full_simplify (simpset()) (read_instantiate
[("f","f"),("a","x - d"),("b","x + d")] isCont_Lb_Ub))) 1);
by Safe_tac;
by (asm_full_simp_tac (simpset() addsimps [abs_le_interval_iff]) 1);
by (subgoal_tac "L \\<le> f x & f x \\<le> M" 1);
by (dres_inst_tac [("P", "%v. ?P v --> ?Q v & ?R v"), ("x","x")] spec 2);
by (Asm_full_simp_tac 2);
by (subgoal_tac "L < f x & f x < M" 1);
by Safe_tac;
by (dres_inst_tac [("x","L")] (ARITH_PROVE "x < y ==> 0 < y - (x::real)") 1);
by (dres_inst_tac [("x","f x")] (ARITH_PROVE "x < y ==> 0 < y - (x::real)") 1);
by (dres_inst_tac [("d1.0","f x - L"),("d2.0","M - f x")]
(real_lbound_gt_zero) 1);
by Safe_tac;
by (res_inst_tac [("x","e")] exI 1);
by Safe_tac;
by (asm_full_simp_tac (simpset() addsimps [abs_le_interval_iff]) 1);
by (dres_inst_tac [("P","%v. ?PP v --> (\\<exists>xa. ?Q v xa)"),("x","y")] spec 1);
by (Step_tac 1 THEN REPEAT(arith_tac 1));
by (res_inst_tac [("x","xa")] exI 1);
by (arith_tac 1);
by (ALLGOALS(etac (ARITH_PROVE "[|x \\<le> y; x \\<noteq> y |] ==> x < (y::real)")));
by (ALLGOALS(rotate_tac 3));
by (dtac lemma_isCont_inj2 1);
by (assume_tac 2);
by (dtac lemma_isCont_inj 3);
by (assume_tac 4);
by (TRYALL(assume_tac));
by Safe_tac;
by (ALLGOALS(dres_inst_tac [("x","z")] spec));
by (ALLGOALS(arith_tac));
qed "isCont_inj_range";
(* ------------------------------------------------------------------------ *)
(* Continuity of inverse function *)
(* ------------------------------------------------------------------------ *)
Goal "[| 0 < d; \\<forall>z. abs(z - x) \\<le> d --> g(f(z)) = z; \
\ \\<forall>z. abs(z - x) \\<le> d --> isCont f z |] \
\ ==> isCont g (f x)";
by (simp_tac (simpset() addsimps [isCont_iff,LIM_def]) 1);
by Safe_tac;
by (dres_inst_tac [("d1.0","r")] (real_lbound_gt_zero) 1);
by (assume_tac 1 THEN Step_tac 1);
by (subgoal_tac "\\<forall>z. abs(z - x) \\<le> e --> (g(f z) = z)" 1);
by (Force_tac 2);
by (subgoal_tac "\\<forall>z. abs(z - x) \\<le> e --> isCont f z" 1);
by (Force_tac 2);
by (dres_inst_tac [("d","e")] isCont_inj_range 1);
by (assume_tac 2 THEN assume_tac 1);
by Safe_tac;
by (res_inst_tac [("x","ea")] exI 1);
by Auto_tac;
by (rotate_tac 4 1);
by (dres_inst_tac [("x","f(x) + xa")] spec 1);
by Auto_tac;
by (dtac sym 1 THEN Auto_tac);
by (arith_tac 1);
qed "isCont_inverse_function";