src/HOL/RealVector.thy
 author webertj Fri, 19 Oct 2012 15:12:52 +0200 changeset 49962 a8cc904a6820 parent 47108 2a1953f0d20d child 50999 3de230ed0547 permissions -rw-r--r--
Renamed {left,right}_distrib to distrib_{right,left}.
```
(*  Title:      HOL/RealVector.thy
Author:     Brian Huffman
*)

header {* Vector Spaces and Algebras over the Reals *}

theory RealVector
imports RComplete
begin

subsection {* Locale for additive functions *}

assumes add: "f (x + y) = f x + f y"
begin

lemma zero: "f 0 = 0"
proof -
have "f 0 = f (0 + 0)" by simp
also have "\<dots> = f 0 + f 0" by (rule add)
finally show "f 0 = 0" by simp
qed

lemma minus: "f (- x) = - f x"
proof -
have "f (- x) + f x = f (- x + x)" by (rule add [symmetric])
also have "\<dots> = - f x + f x" by (simp add: zero)
finally show "f (- x) = - f x" by (rule add_right_imp_eq)
qed

lemma diff: "f (x - y) = f x - f y"

lemma setsum: "f (setsum g A) = (\<Sum>x\<in>A. f (g x))"
apply (cases "finite A")
apply (induct set: finite)
done

end

subsection {* Vector spaces *}

locale vector_space =
fixes scale :: "'a::field \<Rightarrow> 'b::ab_group_add \<Rightarrow> 'b"
assumes scale_right_distrib [algebra_simps]:
"scale a (x + y) = scale a x + scale a y"
and scale_left_distrib [algebra_simps]:
"scale (a + b) x = scale a x + scale b x"
and scale_scale [simp]: "scale a (scale b x) = scale (a * b) x"
and scale_one [simp]: "scale 1 x = x"
begin

lemma scale_left_commute:
"scale a (scale b x) = scale b (scale a x)"

lemma scale_zero_left [simp]: "scale 0 x = 0"
and scale_minus_left [simp]: "scale (- a) x = - (scale a x)"
and scale_left_diff_distrib [algebra_simps]:
"scale (a - b) x = scale a x - scale b x"
and scale_setsum_left: "scale (setsum f A) x = (\<Sum>a\<in>A. scale (f a) x)"
proof -
interpret s: additive "\<lambda>a. scale a x"
proof qed (rule scale_left_distrib)
show "scale 0 x = 0" by (rule s.zero)
show "scale (- a) x = - (scale a x)" by (rule s.minus)
show "scale (a - b) x = scale a x - scale b x" by (rule s.diff)
show "scale (setsum f A) x = (\<Sum>a\<in>A. scale (f a) x)" by (rule s.setsum)
qed

lemma scale_zero_right [simp]: "scale a 0 = 0"
and scale_minus_right [simp]: "scale a (- x) = - (scale a x)"
and scale_right_diff_distrib [algebra_simps]:
"scale a (x - y) = scale a x - scale a y"
and scale_setsum_right: "scale a (setsum f A) = (\<Sum>x\<in>A. scale a (f x))"
proof -
interpret s: additive "\<lambda>x. scale a x"
proof qed (rule scale_right_distrib)
show "scale a 0 = 0" by (rule s.zero)
show "scale a (- x) = - (scale a x)" by (rule s.minus)
show "scale a (x - y) = scale a x - scale a y" by (rule s.diff)
show "scale a (setsum f A) = (\<Sum>x\<in>A. scale a (f x))" by (rule s.setsum)
qed

lemma scale_eq_0_iff [simp]:
"scale a x = 0 \<longleftrightarrow> a = 0 \<or> x = 0"
proof cases
assume "a = 0" thus ?thesis by simp
next
assume anz [simp]: "a \<noteq> 0"
{ assume "scale a x = 0"
hence "scale (inverse a) (scale a x) = 0" by simp
hence "x = 0" by simp }
thus ?thesis by force
qed

lemma scale_left_imp_eq:
"\<lbrakk>a \<noteq> 0; scale a x = scale a y\<rbrakk> \<Longrightarrow> x = y"
proof -
assume nonzero: "a \<noteq> 0"
assume "scale a x = scale a y"
hence "scale a (x - y) = 0"
hence "x - y = 0" by (simp add: nonzero)
thus "x = y" by (simp only: right_minus_eq)
qed

lemma scale_right_imp_eq:
"\<lbrakk>x \<noteq> 0; scale a x = scale b x\<rbrakk> \<Longrightarrow> a = b"
proof -
assume nonzero: "x \<noteq> 0"
assume "scale a x = scale b x"
hence "scale (a - b) x = 0"
hence "a - b = 0" by (simp add: nonzero)
thus "a = b" by (simp only: right_minus_eq)
qed

lemma scale_cancel_left [simp]:
"scale a x = scale a y \<longleftrightarrow> x = y \<or> a = 0"
by (auto intro: scale_left_imp_eq)

lemma scale_cancel_right [simp]:
"scale a x = scale b x \<longleftrightarrow> a = b \<or> x = 0"
by (auto intro: scale_right_imp_eq)

end

subsection {* Real vector spaces *}

class scaleR =
fixes scaleR :: "real \<Rightarrow> 'a \<Rightarrow> 'a" (infixr "*\<^sub>R" 75)
begin

abbreviation
divideR :: "'a \<Rightarrow> real \<Rightarrow> 'a" (infixl "'/\<^sub>R" 70)
where
"x /\<^sub>R r == scaleR (inverse r) x"

end

class real_vector = scaleR + ab_group_add +
assumes scaleR_add_right: "scaleR a (x + y) = scaleR a x + scaleR a y"
and scaleR_add_left: "scaleR (a + b) x = scaleR a x + scaleR b x"
and scaleR_scaleR: "scaleR a (scaleR b x) = scaleR (a * b) x"
and scaleR_one: "scaleR 1 x = x"

interpretation real_vector:
vector_space "scaleR :: real \<Rightarrow> 'a \<Rightarrow> 'a::real_vector"
apply unfold_locales
apply (rule scaleR_scaleR)
apply (rule scaleR_one)
done

text {* Recover original theorem names *}

lemmas scaleR_left_commute = real_vector.scale_left_commute
lemmas scaleR_zero_left = real_vector.scale_zero_left
lemmas scaleR_minus_left = real_vector.scale_minus_left
lemmas scaleR_diff_left = real_vector.scale_left_diff_distrib
lemmas scaleR_setsum_left = real_vector.scale_setsum_left
lemmas scaleR_zero_right = real_vector.scale_zero_right
lemmas scaleR_minus_right = real_vector.scale_minus_right
lemmas scaleR_diff_right = real_vector.scale_right_diff_distrib
lemmas scaleR_setsum_right = real_vector.scale_setsum_right
lemmas scaleR_eq_0_iff = real_vector.scale_eq_0_iff
lemmas scaleR_left_imp_eq = real_vector.scale_left_imp_eq
lemmas scaleR_right_imp_eq = real_vector.scale_right_imp_eq
lemmas scaleR_cancel_left = real_vector.scale_cancel_left
lemmas scaleR_cancel_right = real_vector.scale_cancel_right

text {* Legacy names *}

lemmas scaleR_left_diff_distrib = scaleR_diff_left
lemmas scaleR_right_diff_distrib = scaleR_diff_right

lemma scaleR_minus1_left [simp]:
fixes x :: "'a::real_vector"
shows "scaleR (-1) x = - x"
using scaleR_minus_left [of 1 x] by simp

class real_algebra = real_vector + ring +
assumes mult_scaleR_left [simp]: "scaleR a x * y = scaleR a (x * y)"
and mult_scaleR_right [simp]: "x * scaleR a y = scaleR a (x * y)"

class real_algebra_1 = real_algebra + ring_1

class real_div_algebra = real_algebra_1 + division_ring

class real_field = real_div_algebra + field

instantiation real :: real_field
begin

definition
real_scaleR_def [simp]: "scaleR a x = a * x"

instance proof

end

interpretation scaleR_left: additive "(\<lambda>a. scaleR a x::'a::real_vector)"
proof qed (rule scaleR_left_distrib)

interpretation scaleR_right: additive "(\<lambda>x. scaleR a x::'a::real_vector)"
proof qed (rule scaleR_right_distrib)

lemma nonzero_inverse_scaleR_distrib:
fixes x :: "'a::real_div_algebra" shows
"\<lbrakk>a \<noteq> 0; x \<noteq> 0\<rbrakk> \<Longrightarrow> inverse (scaleR a x) = scaleR (inverse a) (inverse x)"
by (rule inverse_unique, simp)

lemma inverse_scaleR_distrib:
fixes x :: "'a::{real_div_algebra, division_ring_inverse_zero}"
shows "inverse (scaleR a x) = scaleR (inverse a) (inverse x)"
apply (case_tac "a = 0", simp)
apply (case_tac "x = 0", simp)
apply (erule (1) nonzero_inverse_scaleR_distrib)
done

subsection {* Embedding of the Reals into any @{text real_algebra_1}:
@{term of_real} *}

definition
of_real :: "real \<Rightarrow> 'a::real_algebra_1" where
"of_real r = scaleR r 1"

lemma scaleR_conv_of_real: "scaleR r x = of_real r * x"

lemma of_real_0 [simp]: "of_real 0 = 0"

lemma of_real_1 [simp]: "of_real 1 = 1"

lemma of_real_add [simp]: "of_real (x + y) = of_real x + of_real y"

lemma of_real_minus [simp]: "of_real (- x) = - of_real x"

lemma of_real_diff [simp]: "of_real (x - y) = of_real x - of_real y"

lemma of_real_mult [simp]: "of_real (x * y) = of_real x * of_real y"

lemma nonzero_of_real_inverse:
"x \<noteq> 0 \<Longrightarrow> of_real (inverse x) =
inverse (of_real x :: 'a::real_div_algebra)"

lemma of_real_inverse [simp]:
"of_real (inverse x) =
inverse (of_real x :: 'a::{real_div_algebra, division_ring_inverse_zero})"

lemma nonzero_of_real_divide:
"y \<noteq> 0 \<Longrightarrow> of_real (x / y) =
(of_real x / of_real y :: 'a::real_field)"

lemma of_real_divide [simp]:
"of_real (x / y) =
(of_real x / of_real y :: 'a::{real_field, field_inverse_zero})"

lemma of_real_power [simp]:
"of_real (x ^ n) = (of_real x :: 'a::{real_algebra_1}) ^ n"
by (induct n) simp_all

lemma of_real_eq_iff [simp]: "(of_real x = of_real y) = (x = y)"

lemma inj_of_real:
"inj of_real"
by (auto intro: injI)

lemmas of_real_eq_0_iff [simp] = of_real_eq_iff [of _ 0, simplified]

lemma of_real_eq_id [simp]: "of_real = (id :: real \<Rightarrow> real)"
proof
fix r
show "of_real r = id r"
qed

text{*Collapse nested embeddings*}
lemma of_real_of_nat_eq [simp]: "of_real (of_nat n) = of_nat n"
by (induct n) auto

lemma of_real_of_int_eq [simp]: "of_real (of_int z) = of_int z"
by (cases z rule: int_diff_cases, simp)

lemma of_real_numeral: "of_real (numeral w) = numeral w"
using of_real_of_int_eq [of "numeral w"] by simp

lemma of_real_neg_numeral: "of_real (neg_numeral w) = neg_numeral w"
using of_real_of_int_eq [of "neg_numeral w"] by simp

text{*Every real algebra has characteristic zero*}

instance real_algebra_1 < ring_char_0
proof
from inj_of_real inj_of_nat have "inj (of_real \<circ> of_nat)" by (rule inj_comp)
then show "inj (of_nat :: nat \<Rightarrow> 'a)" by (simp add: comp_def)
qed

instance real_field < field_char_0 ..

subsection {* The Set of Real Numbers *}

definition Reals :: "'a::real_algebra_1 set" where
"Reals = range of_real"

notation (xsymbols)
Reals  ("\<real>")

lemma Reals_of_real [simp]: "of_real r \<in> Reals"

lemma Reals_of_int [simp]: "of_int z \<in> Reals"
by (subst of_real_of_int_eq [symmetric], rule Reals_of_real)

lemma Reals_of_nat [simp]: "of_nat n \<in> Reals"
by (subst of_real_of_nat_eq [symmetric], rule Reals_of_real)

lemma Reals_numeral [simp]: "numeral w \<in> Reals"
by (subst of_real_numeral [symmetric], rule Reals_of_real)

lemma Reals_neg_numeral [simp]: "neg_numeral w \<in> Reals"
by (subst of_real_neg_numeral [symmetric], rule Reals_of_real)

lemma Reals_0 [simp]: "0 \<in> Reals"
apply (unfold Reals_def)
apply (rule range_eqI)
apply (rule of_real_0 [symmetric])
done

lemma Reals_1 [simp]: "1 \<in> Reals"
apply (unfold Reals_def)
apply (rule range_eqI)
apply (rule of_real_1 [symmetric])
done

lemma Reals_add [simp]: "\<lbrakk>a \<in> Reals; b \<in> Reals\<rbrakk> \<Longrightarrow> a + b \<in> Reals"
apply (rule range_eqI)
done

lemma Reals_minus [simp]: "a \<in> Reals \<Longrightarrow> - a \<in> Reals"
apply (rule range_eqI)
apply (rule of_real_minus [symmetric])
done

lemma Reals_diff [simp]: "\<lbrakk>a \<in> Reals; b \<in> Reals\<rbrakk> \<Longrightarrow> a - b \<in> Reals"
apply (rule range_eqI)
apply (rule of_real_diff [symmetric])
done

lemma Reals_mult [simp]: "\<lbrakk>a \<in> Reals; b \<in> Reals\<rbrakk> \<Longrightarrow> a * b \<in> Reals"
apply (rule range_eqI)
apply (rule of_real_mult [symmetric])
done

lemma nonzero_Reals_inverse:
fixes a :: "'a::real_div_algebra"
shows "\<lbrakk>a \<in> Reals; a \<noteq> 0\<rbrakk> \<Longrightarrow> inverse a \<in> Reals"
apply (rule range_eqI)
apply (erule nonzero_of_real_inverse [symmetric])
done

lemma Reals_inverse [simp]:
fixes a :: "'a::{real_div_algebra, division_ring_inverse_zero}"
shows "a \<in> Reals \<Longrightarrow> inverse a \<in> Reals"
apply (rule range_eqI)
apply (rule of_real_inverse [symmetric])
done

lemma nonzero_Reals_divide:
fixes a b :: "'a::real_field"
shows "\<lbrakk>a \<in> Reals; b \<in> Reals; b \<noteq> 0\<rbrakk> \<Longrightarrow> a / b \<in> Reals"
apply (rule range_eqI)
apply (erule nonzero_of_real_divide [symmetric])
done

lemma Reals_divide [simp]:
fixes a b :: "'a::{real_field, field_inverse_zero}"
shows "\<lbrakk>a \<in> Reals; b \<in> Reals\<rbrakk> \<Longrightarrow> a / b \<in> Reals"
apply (rule range_eqI)
apply (rule of_real_divide [symmetric])
done

lemma Reals_power [simp]:
fixes a :: "'a::{real_algebra_1}"
shows "a \<in> Reals \<Longrightarrow> a ^ n \<in> Reals"
apply (rule range_eqI)
apply (rule of_real_power [symmetric])
done

lemma Reals_cases [cases set: Reals]:
assumes "q \<in> \<real>"
obtains (of_real) r where "q = of_real r"
unfolding Reals_def
proof -
from `q \<in> \<real>` have "q \<in> range of_real" unfolding Reals_def .
then obtain r where "q = of_real r" ..
then show thesis ..
qed

lemma Reals_induct [case_names of_real, induct set: Reals]:
"q \<in> \<real> \<Longrightarrow> (\<And>r. P (of_real r)) \<Longrightarrow> P q"
by (rule Reals_cases) auto

subsection {* Topological spaces *}

class "open" =
fixes "open" :: "'a set \<Rightarrow> bool"

class topological_space = "open" +
assumes open_UNIV [simp, intro]: "open UNIV"
assumes open_Int [intro]: "open S \<Longrightarrow> open T \<Longrightarrow> open (S \<inter> T)"
assumes open_Union [intro]: "\<forall>S\<in>K. open S \<Longrightarrow> open (\<Union> K)"
begin

definition
closed :: "'a set \<Rightarrow> bool" where
"closed S \<longleftrightarrow> open (- S)"

lemma open_empty [intro, simp]: "open {}"
using open_Union [of "{}"] by simp

lemma open_Un [intro]: "open S \<Longrightarrow> open T \<Longrightarrow> open (S \<union> T)"
using open_Union [of "{S, T}"] by simp

lemma open_UN [intro]: "\<forall>x\<in>A. open (B x) \<Longrightarrow> open (\<Union>x\<in>A. B x)"
unfolding SUP_def by (rule open_Union) auto

lemma open_Inter [intro]: "finite S \<Longrightarrow> \<forall>T\<in>S. open T \<Longrightarrow> open (\<Inter>S)"
by (induct set: finite) auto

lemma open_INT [intro]: "finite A \<Longrightarrow> \<forall>x\<in>A. open (B x) \<Longrightarrow> open (\<Inter>x\<in>A. B x)"
unfolding INF_def by (rule open_Inter) auto

lemma closed_empty [intro, simp]:  "closed {}"
unfolding closed_def by simp

lemma closed_Un [intro]: "closed S \<Longrightarrow> closed T \<Longrightarrow> closed (S \<union> T)"
unfolding closed_def by auto

lemma closed_UNIV [intro, simp]: "closed UNIV"
unfolding closed_def by simp

lemma closed_Int [intro]: "closed S \<Longrightarrow> closed T \<Longrightarrow> closed (S \<inter> T)"
unfolding closed_def by auto

lemma closed_INT [intro]: "\<forall>x\<in>A. closed (B x) \<Longrightarrow> closed (\<Inter>x\<in>A. B x)"
unfolding closed_def by auto

lemma closed_Inter [intro]: "\<forall>S\<in>K. closed S \<Longrightarrow> closed (\<Inter> K)"
unfolding closed_def uminus_Inf by auto

lemma closed_Union [intro]: "finite S \<Longrightarrow> \<forall>T\<in>S. closed T \<Longrightarrow> closed (\<Union>S)"
by (induct set: finite) auto

lemma closed_UN [intro]: "finite A \<Longrightarrow> \<forall>x\<in>A. closed (B x) \<Longrightarrow> closed (\<Union>x\<in>A. B x)"
unfolding SUP_def by (rule closed_Union) auto

lemma open_closed: "open S \<longleftrightarrow> closed (- S)"
unfolding closed_def by simp

lemma closed_open: "closed S \<longleftrightarrow> open (- S)"
unfolding closed_def by simp

lemma open_Diff [intro]: "open S \<Longrightarrow> closed T \<Longrightarrow> open (S - T)"
unfolding closed_open Diff_eq by (rule open_Int)

lemma closed_Diff [intro]: "closed S \<Longrightarrow> open T \<Longrightarrow> closed (S - T)"
unfolding open_closed Diff_eq by (rule closed_Int)

lemma open_Compl [intro]: "closed S \<Longrightarrow> open (- S)"
unfolding closed_open .

lemma closed_Compl [intro]: "open S \<Longrightarrow> closed (- S)"
unfolding open_closed .

end

subsection {* Metric spaces *}

class dist =
fixes dist :: "'a \<Rightarrow> 'a \<Rightarrow> real"

class open_dist = "open" + dist +
assumes open_dist: "open S \<longleftrightarrow> (\<forall>x\<in>S. \<exists>e>0. \<forall>y. dist y x < e \<longrightarrow> y \<in> S)"

class metric_space = open_dist +
assumes dist_eq_0_iff [simp]: "dist x y = 0 \<longleftrightarrow> x = y"
assumes dist_triangle2: "dist x y \<le> dist x z + dist y z"
begin

lemma dist_self [simp]: "dist x x = 0"
by simp

lemma zero_le_dist [simp]: "0 \<le> dist x y"
using dist_triangle2 [of x x y] by simp

lemma zero_less_dist_iff: "0 < dist x y \<longleftrightarrow> x \<noteq> y"

lemma dist_not_less_zero [simp]: "\<not> dist x y < 0"

lemma dist_le_zero_iff [simp]: "dist x y \<le> 0 \<longleftrightarrow> x = y"

lemma dist_commute: "dist x y = dist y x"
proof (rule order_antisym)
show "dist x y \<le> dist y x"
using dist_triangle2 [of x y x] by simp
show "dist y x \<le> dist x y"
using dist_triangle2 [of y x y] by simp
qed

lemma dist_triangle: "dist x z \<le> dist x y + dist y z"
using dist_triangle2 [of x z y] by (simp add: dist_commute)

lemma dist_triangle3: "dist x y \<le> dist a x + dist a y"
using dist_triangle2 [of x y a] by (simp add: dist_commute)

lemma dist_triangle_alt:
shows "dist y z <= dist x y + dist x z"
by (rule dist_triangle3)

lemma dist_pos_lt:
shows "x \<noteq> y ==> 0 < dist x y"

lemma dist_nz:
shows "x \<noteq> y \<longleftrightarrow> 0 < dist x y"

lemma dist_triangle_le:
shows "dist x z + dist y z <= e \<Longrightarrow> dist x y <= e"
by (rule order_trans [OF dist_triangle2])

lemma dist_triangle_lt:
shows "dist x z + dist y z < e ==> dist x y < e"
by (rule le_less_trans [OF dist_triangle2])

lemma dist_triangle_half_l:
shows "dist x1 y < e / 2 \<Longrightarrow> dist x2 y < e / 2 \<Longrightarrow> dist x1 x2 < e"
by (rule dist_triangle_lt [where z=y], simp)

lemma dist_triangle_half_r:
shows "dist y x1 < e / 2 \<Longrightarrow> dist y x2 < e / 2 \<Longrightarrow> dist x1 x2 < e"
by (rule dist_triangle_half_l, simp_all add: dist_commute)

subclass topological_space
proof
have "\<exists>e::real. 0 < e"
by (fast intro: zero_less_one)
then show "open UNIV"
unfolding open_dist by simp
next
fix S T assume "open S" "open T"
then show "open (S \<inter> T)"
unfolding open_dist
apply clarify
apply (drule (1) bspec)+
apply (clarify, rename_tac r s)
apply (rule_tac x="min r s" in exI, simp)
done
next
fix K assume "\<forall>S\<in>K. open S" thus "open (\<Union>K)"
unfolding open_dist by fast
qed

lemma (in metric_space) open_ball: "open {y. dist x y < d}"
proof (unfold open_dist, intro ballI)
fix y assume *: "y \<in> {y. dist x y < d}"
then show "\<exists>e>0. \<forall>z. dist z y < e \<longrightarrow> z \<in> {y. dist x y < d}"
by (auto intro!: exI[of _ "d - dist x y"] simp: field_simps dist_triangle_lt)
qed

end

subsection {* Real normed vector spaces *}

class norm =
fixes norm :: "'a \<Rightarrow> real"

class sgn_div_norm = scaleR + norm + sgn +
assumes sgn_div_norm: "sgn x = x /\<^sub>R norm x"

class dist_norm = dist + norm + minus +
assumes dist_norm: "dist x y = norm (x - y)"

class real_normed_vector = real_vector + sgn_div_norm + dist_norm + open_dist +
assumes norm_ge_zero [simp]: "0 \<le> norm x"
and norm_eq_zero [simp]: "norm x = 0 \<longleftrightarrow> x = 0"
and norm_triangle_ineq: "norm (x + y) \<le> norm x + norm y"
and norm_scaleR [simp]: "norm (scaleR a x) = \<bar>a\<bar> * norm x"

class real_normed_algebra = real_algebra + real_normed_vector +
assumes norm_mult_ineq: "norm (x * y) \<le> norm x * norm y"

class real_normed_algebra_1 = real_algebra_1 + real_normed_algebra +
assumes norm_one [simp]: "norm 1 = 1"

class real_normed_div_algebra = real_div_algebra + real_normed_vector +
assumes norm_mult: "norm (x * y) = norm x * norm y"

class real_normed_field = real_field + real_normed_div_algebra

instance real_normed_div_algebra < real_normed_algebra_1
proof
fix x y :: 'a
show "norm (x * y) \<le> norm x * norm y"
next
have "norm (1 * 1::'a) = norm (1::'a) * norm (1::'a)"
by (rule norm_mult)
thus "norm (1::'a) = 1" by simp
qed

lemma norm_zero [simp]: "norm (0::'a::real_normed_vector) = 0"
by simp

lemma zero_less_norm_iff [simp]:
fixes x :: "'a::real_normed_vector"
shows "(0 < norm x) = (x \<noteq> 0)"

lemma norm_not_less_zero [simp]:
fixes x :: "'a::real_normed_vector"
shows "\<not> norm x < 0"

lemma norm_le_zero_iff [simp]:
fixes x :: "'a::real_normed_vector"
shows "(norm x \<le> 0) = (x = 0)"

lemma norm_minus_cancel [simp]:
fixes x :: "'a::real_normed_vector"
shows "norm (- x) = norm x"
proof -
have "norm (- x) = norm (scaleR (- 1) x)"
by (simp only: scaleR_minus_left scaleR_one)
also have "\<dots> = \<bar>- 1\<bar> * norm x"
by (rule norm_scaleR)
finally show ?thesis by simp
qed

lemma norm_minus_commute:
fixes a b :: "'a::real_normed_vector"
shows "norm (a - b) = norm (b - a)"
proof -
have "norm (- (b - a)) = norm (b - a)"
by (rule norm_minus_cancel)
thus ?thesis by simp
qed

lemma norm_triangle_ineq2:
fixes a b :: "'a::real_normed_vector"
shows "norm a - norm b \<le> norm (a - b)"
proof -
have "norm (a - b + b) \<le> norm (a - b) + norm b"
by (rule norm_triangle_ineq)
thus ?thesis by simp
qed

lemma norm_triangle_ineq3:
fixes a b :: "'a::real_normed_vector"
shows "\<bar>norm a - norm b\<bar> \<le> norm (a - b)"
apply (subst abs_le_iff)
apply auto
apply (rule norm_triangle_ineq2)
apply (subst norm_minus_commute)
apply (rule norm_triangle_ineq2)
done

lemma norm_triangle_ineq4:
fixes a b :: "'a::real_normed_vector"
shows "norm (a - b) \<le> norm a + norm b"
proof -
have "norm (a + - b) \<le> norm a + norm (- b)"
by (rule norm_triangle_ineq)
thus ?thesis
by (simp only: diff_minus norm_minus_cancel)
qed

lemma norm_diff_ineq:
fixes a b :: "'a::real_normed_vector"
shows "norm a - norm b \<le> norm (a + b)"
proof -
have "norm a - norm (- b) \<le> norm (a - - b)"
by (rule norm_triangle_ineq2)
thus ?thesis by simp
qed

lemma norm_diff_triangle_ineq:
fixes a b c d :: "'a::real_normed_vector"
shows "norm ((a + b) - (c + d)) \<le> norm (a - c) + norm (b - d)"
proof -
have "norm ((a + b) - (c + d)) = norm ((a - c) + (b - d))"
also have "\<dots> \<le> norm (a - c) + norm (b - d)"
by (rule norm_triangle_ineq)
finally show ?thesis .
qed

lemma abs_norm_cancel [simp]:
fixes a :: "'a::real_normed_vector"
shows "\<bar>norm a\<bar> = norm a"
by (rule abs_of_nonneg [OF norm_ge_zero])

fixes x y :: "'a::real_normed_vector"
shows "\<lbrakk>norm x < r; norm y < s\<rbrakk> \<Longrightarrow> norm (x + y) < r + s"
by (rule order_le_less_trans [OF norm_triangle_ineq add_strict_mono])

lemma norm_mult_less:
fixes x y :: "'a::real_normed_algebra"
shows "\<lbrakk>norm x < r; norm y < s\<rbrakk> \<Longrightarrow> norm (x * y) < r * s"
apply (rule order_le_less_trans [OF norm_mult_ineq])
done

lemma norm_of_real [simp]:
"norm (of_real r :: 'a::real_normed_algebra_1) = \<bar>r\<bar>"
unfolding of_real_def by simp

lemma norm_numeral [simp]:
"norm (numeral w::'a::real_normed_algebra_1) = numeral w"
by (subst of_real_numeral [symmetric], subst norm_of_real, simp)

lemma norm_neg_numeral [simp]:
"norm (neg_numeral w::'a::real_normed_algebra_1) = numeral w"
by (subst of_real_neg_numeral [symmetric], subst norm_of_real, simp)

lemma norm_of_int [simp]:
"norm (of_int z::'a::real_normed_algebra_1) = \<bar>of_int z\<bar>"
by (subst of_real_of_int_eq [symmetric], rule norm_of_real)

lemma norm_of_nat [simp]:
"norm (of_nat n::'a::real_normed_algebra_1) = of_nat n"
apply (subst of_real_of_nat_eq [symmetric])
apply (subst norm_of_real, simp)
done

lemma nonzero_norm_inverse:
fixes a :: "'a::real_normed_div_algebra"
shows "a \<noteq> 0 \<Longrightarrow> norm (inverse a) = inverse (norm a)"
apply (rule inverse_unique [symmetric])
done

lemma norm_inverse:
fixes a :: "'a::{real_normed_div_algebra, division_ring_inverse_zero}"
shows "norm (inverse a) = inverse (norm a)"
apply (case_tac "a = 0", simp)
apply (erule nonzero_norm_inverse)
done

lemma nonzero_norm_divide:
fixes a b :: "'a::real_normed_field"
shows "b \<noteq> 0 \<Longrightarrow> norm (a / b) = norm a / norm b"
by (simp add: divide_inverse norm_mult nonzero_norm_inverse)

lemma norm_divide:
fixes a b :: "'a::{real_normed_field, field_inverse_zero}"
shows "norm (a / b) = norm a / norm b"
by (simp add: divide_inverse norm_mult norm_inverse)

lemma norm_power_ineq:
fixes x :: "'a::{real_normed_algebra_1}"
shows "norm (x ^ n) \<le> norm x ^ n"
proof (induct n)
case 0 show "norm (x ^ 0) \<le> norm x ^ 0" by simp
next
case (Suc n)
have "norm (x * x ^ n) \<le> norm x * norm (x ^ n)"
by (rule norm_mult_ineq)
also from Suc have "\<dots> \<le> norm x * norm x ^ n"
using norm_ge_zero by (rule mult_left_mono)
finally show "norm (x ^ Suc n) \<le> norm x ^ Suc n"
by simp
qed

lemma norm_power:
fixes x :: "'a::{real_normed_div_algebra}"
shows "norm (x ^ n) = norm x ^ n"
by (induct n) (simp_all add: norm_mult)

text {* Every normed vector space is a metric space. *}

instance real_normed_vector < metric_space
proof
fix x y :: 'a show "dist x y = 0 \<longleftrightarrow> x = y"
unfolding dist_norm by simp
next
fix x y z :: 'a show "dist x y \<le> dist x z + dist y z"
unfolding dist_norm
using norm_triangle_ineq4 [of "x - z" "y - z"] by simp
qed

subsection {* Class instances for real numbers *}

instantiation real :: real_normed_field
begin

definition real_norm_def [simp]:
"norm r = \<bar>r\<bar>"

definition dist_real_def:
"dist x y = \<bar>x - y\<bar>"

definition open_real_def:
"open (S :: real set) \<longleftrightarrow> (\<forall>x\<in>S. \<exists>e>0. \<forall>y. dist y x < e \<longrightarrow> y \<in> S)"

instance
apply (intro_classes, unfold real_norm_def real_scaleR_def)
apply (rule dist_real_def)
apply (rule open_real_def)
apply (rule abs_ge_zero)
apply (rule abs_eq_0)
apply (rule abs_triangle_ineq)
apply (rule abs_mult)
apply (rule abs_mult)
done

end

lemma open_real_lessThan [simp]:
fixes a :: real shows "open {..<a}"
unfolding open_real_def dist_real_def
proof (clarify)
fix x assume "x < a"
hence "0 < a - x \<and> (\<forall>y. \<bar>y - x\<bar> < a - x \<longrightarrow> y \<in> {..<a})" by auto
thus "\<exists>e>0. \<forall>y. \<bar>y - x\<bar> < e \<longrightarrow> y \<in> {..<a}" ..
qed

lemma open_real_greaterThan [simp]:
fixes a :: real shows "open {a<..}"
unfolding open_real_def dist_real_def
proof (clarify)
fix x assume "a < x"
hence "0 < x - a \<and> (\<forall>y. \<bar>y - x\<bar> < x - a \<longrightarrow> y \<in> {a<..})" by auto
thus "\<exists>e>0. \<forall>y. \<bar>y - x\<bar> < e \<longrightarrow> y \<in> {a<..}" ..
qed

lemma open_real_greaterThanLessThan [simp]:
fixes a b :: real shows "open {a<..<b}"
proof -
have "{a<..<b} = {a<..} \<inter> {..<b}" by auto
thus "open {a<..<b}" by (simp add: open_Int)
qed

lemma closed_real_atMost [simp]:
fixes a :: real shows "closed {..a}"
unfolding closed_open by simp

lemma closed_real_atLeast [simp]:
fixes a :: real shows "closed {a..}"
unfolding closed_open by simp

lemma closed_real_atLeastAtMost [simp]:
fixes a b :: real shows "closed {a..b}"
proof -
have "{a..b} = {a..} \<inter> {..b}" by auto
thus "closed {a..b}" by (simp add: closed_Int)
qed

subsection {* Extra type constraints *}

text {* Only allow @{term "open"} in class @{text topological_space}. *}

(@{const_name "open"}, SOME @{typ "'a::topological_space set \<Rightarrow> bool"}) *}

text {* Only allow @{term dist} in class @{text metric_space}. *}

(@{const_name dist}, SOME @{typ "'a::metric_space \<Rightarrow> 'a \<Rightarrow> real"}) *}

text {* Only allow @{term norm} in class @{text real_normed_vector}. *}

(@{const_name norm}, SOME @{typ "'a::real_normed_vector \<Rightarrow> real"}) *}

subsection {* Sign function *}

lemma norm_sgn:
"norm (sgn(x::'a::real_normed_vector)) = (if x = 0 then 0 else 1)"

lemma sgn_zero [simp]: "sgn(0::'a::real_normed_vector) = 0"

lemma sgn_zero_iff: "(sgn(x::'a::real_normed_vector) = 0) = (x = 0)"

lemma sgn_minus: "sgn (- x) = - sgn(x::'a::real_normed_vector)"

lemma sgn_scaleR:
"sgn (scaleR r x) = scaleR (sgn r) (sgn(x::'a::real_normed_vector))"

lemma sgn_one [simp]: "sgn (1::'a::real_normed_algebra_1) = 1"

lemma sgn_of_real:
"sgn (of_real r::'a::real_normed_algebra_1) = of_real (sgn r)"
unfolding of_real_def by (simp only: sgn_scaleR sgn_one)

lemma sgn_mult:
fixes x y :: "'a::real_normed_div_algebra"
shows "sgn (x * y) = sgn x * sgn y"
by (simp add: sgn_div_norm norm_mult mult_commute)

lemma real_sgn_eq: "sgn (x::real) = x / \<bar>x\<bar>"

lemma real_sgn_pos: "0 < (x::real) \<Longrightarrow> sgn x = 1"
unfolding real_sgn_eq by simp

lemma real_sgn_neg: "(x::real) < 0 \<Longrightarrow> sgn x = -1"
unfolding real_sgn_eq by simp

subsection {* Bounded Linear and Bilinear Operators *}

locale bounded_linear = additive f for f :: "'a::real_normed_vector \<Rightarrow> 'b::real_normed_vector" +
assumes scaleR: "f (scaleR r x) = scaleR r (f x)"
assumes bounded: "\<exists>K. \<forall>x. norm (f x) \<le> norm x * K"
begin

lemma pos_bounded:
"\<exists>K>0. \<forall>x. norm (f x) \<le> norm x * K"
proof -
obtain K where K: "\<And>x. norm (f x) \<le> norm x * K"
using bounded by fast
show ?thesis
proof (intro exI impI conjI allI)
show "0 < max 1 K"
by (rule order_less_le_trans [OF zero_less_one le_maxI1])
next
fix x
have "norm (f x) \<le> norm x * K" using K .
also have "\<dots> \<le> norm x * max 1 K"
by (rule mult_left_mono [OF le_maxI2 norm_ge_zero])
finally show "norm (f x) \<le> norm x * max 1 K" .
qed
qed

lemma nonneg_bounded:
"\<exists>K\<ge>0. \<forall>x. norm (f x) \<le> norm x * K"
proof -
from pos_bounded
show ?thesis by (auto intro: order_less_imp_le)
qed

end

lemma bounded_linear_intro:
assumes "\<And>x y. f (x + y) = f x + f y"
assumes "\<And>r x. f (scaleR r x) = scaleR r (f x)"
assumes "\<And>x. norm (f x) \<le> norm x * K"
shows "bounded_linear f"
by default (fast intro: assms)+

locale bounded_bilinear =
fixes prod :: "['a::real_normed_vector, 'b::real_normed_vector]
\<Rightarrow> 'c::real_normed_vector"
(infixl "**" 70)
assumes add_left: "prod (a + a') b = prod a b + prod a' b"
assumes add_right: "prod a (b + b') = prod a b + prod a b'"
assumes scaleR_left: "prod (scaleR r a) b = scaleR r (prod a b)"
assumes scaleR_right: "prod a (scaleR r b) = scaleR r (prod a b)"
assumes bounded: "\<exists>K. \<forall>a b. norm (prod a b) \<le> norm a * norm b * K"
begin

lemma pos_bounded:
"\<exists>K>0. \<forall>a b. norm (a ** b) \<le> norm a * norm b * K"
apply (cut_tac bounded, erule exE)
apply (rule_tac x="max 1 K" in exI, safe)
apply (rule order_less_le_trans [OF zero_less_one le_maxI1])
apply (drule spec, drule spec, erule order_trans)
apply (rule mult_left_mono [OF le_maxI2])
apply (intro mult_nonneg_nonneg norm_ge_zero)
done

lemma nonneg_bounded:
"\<exists>K\<ge>0. \<forall>a b. norm (a ** b) \<le> norm a * norm b * K"
proof -
from pos_bounded
show ?thesis by (auto intro: order_less_imp_le)
qed

lemma zero_left: "prod 0 b = 0"

lemma zero_right: "prod a 0 = 0"

lemma minus_left: "prod (- a) b = - prod a b"

lemma minus_right: "prod a (- b) = - prod a b"

lemma diff_left:
"prod (a - a') b = prod a b - prod a' b"

lemma diff_right:
"prod a (b - b') = prod a b - prod a b'"

lemma bounded_linear_left:
"bounded_linear (\<lambda>a. a ** b)"
apply (cut_tac bounded, safe)
apply (rule_tac K="norm b * K" in bounded_linear_intro)
apply (rule scaleR_left)
done

lemma bounded_linear_right:
"bounded_linear (\<lambda>b. a ** b)"
apply (cut_tac bounded, safe)
apply (rule_tac K="norm a * K" in bounded_linear_intro)
apply (rule scaleR_right)
done

lemma prod_diff_prod:
"(x ** y - a ** b) = (x - a) ** (y - b) + (x - a) ** b + a ** (y - b)"

end

lemma bounded_bilinear_mult:
"bounded_bilinear (op * :: 'a \<Rightarrow> 'a \<Rightarrow> 'a::real_normed_algebra)"
apply (rule bounded_bilinear.intro)
apply (rule distrib_right)
apply (rule distrib_left)
apply (rule mult_scaleR_left)
apply (rule mult_scaleR_right)
apply (rule_tac x="1" in exI)
done

lemma bounded_linear_mult_left:
"bounded_linear (\<lambda>x::'a::real_normed_algebra. x * y)"
using bounded_bilinear_mult
by (rule bounded_bilinear.bounded_linear_left)

lemma bounded_linear_mult_right:
"bounded_linear (\<lambda>y::'a::real_normed_algebra. x * y)"
using bounded_bilinear_mult
by (rule bounded_bilinear.bounded_linear_right)

lemma bounded_linear_divide:
"bounded_linear (\<lambda>x::'a::real_normed_field. x / y)"
unfolding divide_inverse by (rule bounded_linear_mult_left)

lemma bounded_bilinear_scaleR: "bounded_bilinear scaleR"
apply (rule bounded_bilinear.intro)
apply (rule scaleR_left_distrib)
apply (rule scaleR_right_distrib)
apply simp
apply (rule scaleR_left_commute)
apply (rule_tac x="1" in exI, simp)
done

lemma bounded_linear_scaleR_left: "bounded_linear (\<lambda>r. scaleR r x)"
using bounded_bilinear_scaleR
by (rule bounded_bilinear.bounded_linear_left)

lemma bounded_linear_scaleR_right: "bounded_linear (\<lambda>x. scaleR r x)"
using bounded_bilinear_scaleR
by (rule bounded_bilinear.bounded_linear_right)

lemma bounded_linear_of_real: "bounded_linear (\<lambda>r. of_real r)"
unfolding of_real_def by (rule bounded_linear_scaleR_left)

subsection{* Hausdorff and other separation properties *}

class t0_space = topological_space +
assumes t0_space: "x \<noteq> y \<Longrightarrow> \<exists>U. open U \<and> \<not> (x \<in> U \<longleftrightarrow> y \<in> U)"

class t1_space = topological_space +
assumes t1_space: "x \<noteq> y \<Longrightarrow> \<exists>U. open U \<and> x \<in> U \<and> y \<notin> U"

instance t1_space \<subseteq> t0_space
proof qed (fast dest: t1_space)

lemma separation_t1:
fixes x y :: "'a::t1_space"
shows "x \<noteq> y \<longleftrightarrow> (\<exists>U. open U \<and> x \<in> U \<and> y \<notin> U)"
using t1_space[of x y] by blast

lemma closed_singleton:
fixes a :: "'a::t1_space"
shows "closed {a}"
proof -
let ?T = "\<Union>{S. open S \<and> a \<notin> S}"
have "open ?T" by (simp add: open_Union)
also have "?T = - {a}"
by (simp add: set_eq_iff separation_t1, auto)
finally show "closed {a}" unfolding closed_def .
qed

lemma closed_insert [simp]:
fixes a :: "'a::t1_space"
assumes "closed S" shows "closed (insert a S)"
proof -
from closed_singleton assms
have "closed ({a} \<union> S)" by (rule closed_Un)
thus "closed (insert a S)" by simp
qed

lemma finite_imp_closed:
fixes S :: "'a::t1_space set"
shows "finite S \<Longrightarrow> closed S"
by (induct set: finite, simp_all)

text {* T2 spaces are also known as Hausdorff spaces. *}

class t2_space = topological_space +
assumes hausdorff: "x \<noteq> y \<Longrightarrow> \<exists>U V. open U \<and> open V \<and> x \<in> U \<and> y \<in> V \<and> U \<inter> V = {}"

instance t2_space \<subseteq> t1_space
proof qed (fast dest: hausdorff)

instance metric_space \<subseteq> t2_space
proof
fix x y :: "'a::metric_space"
assume xy: "x \<noteq> y"
let ?U = "{y'. dist x y' < dist x y / 2}"
let ?V = "{x'. dist y x' < dist x y / 2}"
have th0: "\<And>d x y z. (d x z :: real) \<le> d x y + d y z \<Longrightarrow> d y z = d z y
\<Longrightarrow> \<not>(d x y * 2 < d x z \<and> d z y * 2 < d x z)" by arith
have "open ?U \<and> open ?V \<and> x \<in> ?U \<and> y \<in> ?V \<and> ?U \<inter> ?V = {}"
using dist_pos_lt[OF xy] th0[of dist, OF dist_triangle dist_commute]
using open_ball[of _ "dist x y / 2"] by auto
then show "\<exists>U V. open U \<and> open V \<and> x \<in> U \<and> y \<in> V \<and> U \<inter> V = {}"
by blast
qed

lemma separation_t2:
fixes x y :: "'a::t2_space"
shows "x \<noteq> y \<longleftrightarrow> (\<exists>U V. open U \<and> open V \<and> x \<in> U \<and> y \<in> V \<and> U \<inter> V = {})"
using hausdorff[of x y] by blast

lemma separation_t0:
fixes x y :: "'a::t0_space"
shows "x \<noteq> y \<longleftrightarrow> (\<exists>U. open U \<and> ~(x\<in>U \<longleftrightarrow> y\<in>U))"
using t0_space[of x y] by blast

text {* A perfect space is a topological space with no isolated points. *}

class perfect_space = topological_space +
assumes not_open_singleton: "\<not> open {x}"

instance real_normed_algebra_1 \<subseteq> perfect_space
proof
fix x::'a
show "\<not> open {x}"
unfolding open_dist dist_norm
by (clarsimp, rule_tac x="x + of_real (e/2)" in exI, simp)
qed

end
```