(* Title: HOL/Rings.thy
Author: Gertrud Bauer
Author: Steven Obua
Author: Tobias Nipkow
Author: Lawrence C Paulson
Author: Markus Wenzel
Author: Jeremy Avigad
*)
header {* Rings *}
theory Rings
imports Groups
begin
class semiring = ab_semigroup_add + semigroup_mult +
assumes distrib_right[algebra_simps, field_simps]: "(a + b) * c = a * c + b * c"
assumes distrib_left[algebra_simps, field_simps]: "a * (b + c) = a * b + a * c"
begin
text{*For the @{text combine_numerals} simproc*}
lemma combine_common_factor:
"a * e + (b * e + c) = (a + b) * e + c"
by (simp add: distrib_right add_ac)
end
class mult_zero = times + zero +
assumes mult_zero_left [simp]: "0 * a = 0"
assumes mult_zero_right [simp]: "a * 0 = 0"
class semiring_0 = semiring + comm_monoid_add + mult_zero
class semiring_0_cancel = semiring + cancel_comm_monoid_add
begin
subclass semiring_0
proof
fix a :: 'a
have "0 * a + 0 * a = 0 * a + 0" by (simp add: distrib_right [symmetric])
thus "0 * a = 0" by (simp only: add_left_cancel)
next
fix a :: 'a
have "a * 0 + a * 0 = a * 0 + 0" by (simp add: distrib_left [symmetric])
thus "a * 0 = 0" by (simp only: add_left_cancel)
qed
end
class comm_semiring = ab_semigroup_add + ab_semigroup_mult +
assumes distrib: "(a + b) * c = a * c + b * c"
begin
subclass semiring
proof
fix a b c :: 'a
show "(a + b) * c = a * c + b * c" by (simp add: distrib)
have "a * (b + c) = (b + c) * a" by (simp add: mult_ac)
also have "... = b * a + c * a" by (simp only: distrib)
also have "... = a * b + a * c" by (simp add: mult_ac)
finally show "a * (b + c) = a * b + a * c" by blast
qed
end
class comm_semiring_0 = comm_semiring + comm_monoid_add + mult_zero
begin
subclass semiring_0 ..
end
class comm_semiring_0_cancel = comm_semiring + cancel_comm_monoid_add
begin
subclass semiring_0_cancel ..
subclass comm_semiring_0 ..
end
class zero_neq_one = zero + one +
assumes zero_neq_one [simp]: "0 \<noteq> 1"
begin
lemma one_neq_zero [simp]: "1 \<noteq> 0"
by (rule not_sym) (rule zero_neq_one)
definition of_bool :: "bool \<Rightarrow> 'a"
where
"of_bool p = (if p then 1 else 0)"
lemma of_bool_eq [simp, code]:
"of_bool False = 0"
"of_bool True = 1"
by (simp_all add: of_bool_def)
lemma of_bool_eq_iff:
"of_bool p = of_bool q \<longleftrightarrow> p = q"
by (simp add: of_bool_def)
lemma split_of_bool [split]:
"P (of_bool p) \<longleftrightarrow> (p \<longrightarrow> P 1) \<and> (\<not> p \<longrightarrow> P 0)"
by (cases p) simp_all
lemma split_of_bool_asm:
"P (of_bool p) \<longleftrightarrow> \<not> (p \<and> \<not> P 1 \<or> \<not> p \<and> \<not> P 0)"
by (cases p) simp_all
end
class semiring_1 = zero_neq_one + semiring_0 + monoid_mult
text {* Abstract divisibility *}
class dvd = times
begin
definition dvd :: "'a \<Rightarrow> 'a \<Rightarrow> bool" (infix "dvd" 50) where
"b dvd a \<longleftrightarrow> (\<exists>k. a = b * k)"
lemma dvdI [intro?]: "a = b * k \<Longrightarrow> b dvd a"
unfolding dvd_def ..
lemma dvdE [elim?]: "b dvd a \<Longrightarrow> (\<And>k. a = b * k \<Longrightarrow> P) \<Longrightarrow> P"
unfolding dvd_def by blast
end
class comm_semiring_1 = zero_neq_one + comm_semiring_0 + comm_monoid_mult + dvd
(*previously almost_semiring*)
begin
subclass semiring_1 ..
lemma dvd_refl[simp]: "a dvd a"
proof
show "a = a * 1" by simp
qed
lemma dvd_trans:
assumes "a dvd b" and "b dvd c"
shows "a dvd c"
proof -
from assms obtain v where "b = a * v" by (auto elim!: dvdE)
moreover from assms obtain w where "c = b * w" by (auto elim!: dvdE)
ultimately have "c = a * (v * w)" by (simp add: mult_assoc)
then show ?thesis ..
qed
lemma dvd_0_left_iff [simp]: "0 dvd a \<longleftrightarrow> a = 0"
by (auto intro: dvd_refl elim!: dvdE)
lemma dvd_0_right [iff]: "a dvd 0"
proof
show "0 = a * 0" by simp
qed
lemma one_dvd [simp]: "1 dvd a"
by (auto intro!: dvdI)
lemma dvd_mult[simp]: "a dvd c \<Longrightarrow> a dvd (b * c)"
by (auto intro!: mult_left_commute dvdI elim!: dvdE)
lemma dvd_mult2[simp]: "a dvd b \<Longrightarrow> a dvd (b * c)"
apply (subst mult_commute)
apply (erule dvd_mult)
done
lemma dvd_triv_right [simp]: "a dvd b * a"
by (rule dvd_mult) (rule dvd_refl)
lemma dvd_triv_left [simp]: "a dvd a * b"
by (rule dvd_mult2) (rule dvd_refl)
lemma mult_dvd_mono:
assumes "a dvd b"
and "c dvd d"
shows "a * c dvd b * d"
proof -
from `a dvd b` obtain b' where "b = a * b'" ..
moreover from `c dvd d` obtain d' where "d = c * d'" ..
ultimately have "b * d = (a * c) * (b' * d')" by (simp add: mult_ac)
then show ?thesis ..
qed
lemma dvd_mult_left: "a * b dvd c \<Longrightarrow> a dvd c"
by (simp add: dvd_def mult_assoc, blast)
lemma dvd_mult_right: "a * b dvd c \<Longrightarrow> b dvd c"
unfolding mult_ac [of a] by (rule dvd_mult_left)
lemma dvd_0_left: "0 dvd a \<Longrightarrow> a = 0"
by simp
lemma dvd_add[simp]:
assumes "a dvd b" and "a dvd c" shows "a dvd (b + c)"
proof -
from `a dvd b` obtain b' where "b = a * b'" ..
moreover from `a dvd c` obtain c' where "c = a * c'" ..
ultimately have "b + c = a * (b' + c')" by (simp add: distrib_left)
then show ?thesis ..
qed
end
class no_zero_divisors = zero + times +
assumes no_zero_divisors: "a \<noteq> 0 \<Longrightarrow> b \<noteq> 0 \<Longrightarrow> a * b \<noteq> 0"
begin
lemma divisors_zero:
assumes "a * b = 0"
shows "a = 0 \<or> b = 0"
proof (rule classical)
assume "\<not> (a = 0 \<or> b = 0)"
then have "a \<noteq> 0" and "b \<noteq> 0" by auto
with no_zero_divisors have "a * b \<noteq> 0" by blast
with assms show ?thesis by simp
qed
end
class semiring_1_cancel = semiring + cancel_comm_monoid_add
+ zero_neq_one + monoid_mult
begin
subclass semiring_0_cancel ..
subclass semiring_1 ..
end
class comm_semiring_1_cancel = comm_semiring + cancel_comm_monoid_add
+ zero_neq_one + comm_monoid_mult
begin
subclass semiring_1_cancel ..
subclass comm_semiring_0_cancel ..
subclass comm_semiring_1 ..
end
class ring = semiring + ab_group_add
begin
subclass semiring_0_cancel ..
text {* Distribution rules *}
lemma minus_mult_left: "- (a * b) = - a * b"
by (rule minus_unique) (simp add: distrib_right [symmetric])
lemma minus_mult_right: "- (a * b) = a * - b"
by (rule minus_unique) (simp add: distrib_left [symmetric])
text{*Extract signs from products*}
lemmas mult_minus_left [simp] = minus_mult_left [symmetric]
lemmas mult_minus_right [simp] = minus_mult_right [symmetric]
lemma minus_mult_minus [simp]: "- a * - b = a * b"
by simp
lemma minus_mult_commute: "- a * b = a * - b"
by simp
lemma right_diff_distrib [algebra_simps, field_simps]:
"a * (b - c) = a * b - a * c"
using distrib_left [of a b "-c "] by simp
lemma left_diff_distrib [algebra_simps, field_simps]:
"(a - b) * c = a * c - b * c"
using distrib_right [of a "- b" c] by simp
lemmas ring_distribs =
distrib_left distrib_right left_diff_distrib right_diff_distrib
lemma eq_add_iff1:
"a * e + c = b * e + d \<longleftrightarrow> (a - b) * e + c = d"
by (simp add: algebra_simps)
lemma eq_add_iff2:
"a * e + c = b * e + d \<longleftrightarrow> c = (b - a) * e + d"
by (simp add: algebra_simps)
end
lemmas ring_distribs =
distrib_left distrib_right left_diff_distrib right_diff_distrib
class comm_ring = comm_semiring + ab_group_add
begin
subclass ring ..
subclass comm_semiring_0_cancel ..
lemma square_diff_square_factored:
"x * x - y * y = (x + y) * (x - y)"
by (simp add: algebra_simps)
end
class ring_1 = ring + zero_neq_one + monoid_mult
begin
subclass semiring_1_cancel ..
lemma square_diff_one_factored:
"x * x - 1 = (x + 1) * (x - 1)"
by (simp add: algebra_simps)
end
class comm_ring_1 = comm_ring + zero_neq_one + comm_monoid_mult
(*previously ring*)
begin
subclass ring_1 ..
subclass comm_semiring_1_cancel ..
lemma dvd_minus_iff [simp]: "x dvd - y \<longleftrightarrow> x dvd y"
proof
assume "x dvd - y"
then have "x dvd - 1 * - y" by (rule dvd_mult)
then show "x dvd y" by simp
next
assume "x dvd y"
then have "x dvd - 1 * y" by (rule dvd_mult)
then show "x dvd - y" by simp
qed
lemma minus_dvd_iff [simp]: "- x dvd y \<longleftrightarrow> x dvd y"
proof
assume "- x dvd y"
then obtain k where "y = - x * k" ..
then have "y = x * - k" by simp
then show "x dvd y" ..
next
assume "x dvd y"
then obtain k where "y = x * k" ..
then have "y = - x * - k" by simp
then show "- x dvd y" ..
qed
lemma dvd_diff [simp]:
"x dvd y \<Longrightarrow> x dvd z \<Longrightarrow> x dvd (y - z)"
using dvd_add [of x y "- z"] by simp
end
class ring_no_zero_divisors = ring + no_zero_divisors
begin
lemma mult_eq_0_iff [simp]:
shows "a * b = 0 \<longleftrightarrow> (a = 0 \<or> b = 0)"
proof (cases "a = 0 \<or> b = 0")
case False then have "a \<noteq> 0" and "b \<noteq> 0" by auto
then show ?thesis using no_zero_divisors by simp
next
case True then show ?thesis by auto
qed
text{*Cancellation of equalities with a common factor*}
lemma mult_cancel_right [simp]:
"a * c = b * c \<longleftrightarrow> c = 0 \<or> a = b"
proof -
have "(a * c = b * c) = ((a - b) * c = 0)"
by (simp add: algebra_simps)
thus ?thesis by (simp add: disj_commute)
qed
lemma mult_cancel_left [simp]:
"c * a = c * b \<longleftrightarrow> c = 0 \<or> a = b"
proof -
have "(c * a = c * b) = (c * (a - b) = 0)"
by (simp add: algebra_simps)
thus ?thesis by simp
qed
lemma mult_left_cancel: "c \<noteq> 0 \<Longrightarrow> (c*a=c*b) = (a=b)"
by simp
lemma mult_right_cancel: "c \<noteq> 0 \<Longrightarrow> (a*c=b*c) = (a=b)"
by simp
end
class ring_1_no_zero_divisors = ring_1 + ring_no_zero_divisors
begin
lemma square_eq_1_iff:
"x * x = 1 \<longleftrightarrow> x = 1 \<or> x = - 1"
proof -
have "(x - 1) * (x + 1) = x * x - 1"
by (simp add: algebra_simps)
hence "x * x = 1 \<longleftrightarrow> (x - 1) * (x + 1) = 0"
by simp
thus ?thesis
by (simp add: eq_neg_iff_add_eq_0)
qed
lemma mult_cancel_right1 [simp]:
"c = b * c \<longleftrightarrow> c = 0 \<or> b = 1"
by (insert mult_cancel_right [of 1 c b], force)
lemma mult_cancel_right2 [simp]:
"a * c = c \<longleftrightarrow> c = 0 \<or> a = 1"
by (insert mult_cancel_right [of a c 1], simp)
lemma mult_cancel_left1 [simp]:
"c = c * b \<longleftrightarrow> c = 0 \<or> b = 1"
by (insert mult_cancel_left [of c 1 b], force)
lemma mult_cancel_left2 [simp]:
"c * a = c \<longleftrightarrow> c = 0 \<or> a = 1"
by (insert mult_cancel_left [of c a 1], simp)
end
class idom = comm_ring_1 + no_zero_divisors
begin
subclass ring_1_no_zero_divisors ..
lemma square_eq_iff: "a * a = b * b \<longleftrightarrow> (a = b \<or> a = - b)"
proof
assume "a * a = b * b"
then have "(a - b) * (a + b) = 0"
by (simp add: algebra_simps)
then show "a = b \<or> a = - b"
by (simp add: eq_neg_iff_add_eq_0)
next
assume "a = b \<or> a = - b"
then show "a * a = b * b" by auto
qed
lemma dvd_mult_cancel_right [simp]:
"a * c dvd b * c \<longleftrightarrow> c = 0 \<or> a dvd b"
proof -
have "a * c dvd b * c \<longleftrightarrow> (\<exists>k. b * c = (a * k) * c)"
unfolding dvd_def by (simp add: mult_ac)
also have "(\<exists>k. b * c = (a * k) * c) \<longleftrightarrow> c = 0 \<or> a dvd b"
unfolding dvd_def by simp
finally show ?thesis .
qed
lemma dvd_mult_cancel_left [simp]:
"c * a dvd c * b \<longleftrightarrow> c = 0 \<or> a dvd b"
proof -
have "c * a dvd c * b \<longleftrightarrow> (\<exists>k. b * c = (a * k) * c)"
unfolding dvd_def by (simp add: mult_ac)
also have "(\<exists>k. b * c = (a * k) * c) \<longleftrightarrow> c = 0 \<or> a dvd b"
unfolding dvd_def by simp
finally show ?thesis .
qed
end
text {*
The theory of partially ordered rings is taken from the books:
\begin{itemize}
\item \emph{Lattice Theory} by Garret Birkhoff, American Mathematical Society 1979
\item \emph{Partially Ordered Algebraic Systems}, Pergamon Press 1963
\end{itemize}
Most of the used notions can also be looked up in
\begin{itemize}
\item @{url "http://www.mathworld.com"} by Eric Weisstein et. al.
\item \emph{Algebra I} by van der Waerden, Springer.
\end{itemize}
*}
class ordered_semiring = semiring + comm_monoid_add + ordered_ab_semigroup_add +
assumes mult_left_mono: "a \<le> b \<Longrightarrow> 0 \<le> c \<Longrightarrow> c * a \<le> c * b"
assumes mult_right_mono: "a \<le> b \<Longrightarrow> 0 \<le> c \<Longrightarrow> a * c \<le> b * c"
begin
lemma mult_mono:
"a \<le> b \<Longrightarrow> c \<le> d \<Longrightarrow> 0 \<le> b \<Longrightarrow> 0 \<le> c \<Longrightarrow> a * c \<le> b * d"
apply (erule mult_right_mono [THEN order_trans], assumption)
apply (erule mult_left_mono, assumption)
done
lemma mult_mono':
"a \<le> b \<Longrightarrow> c \<le> d \<Longrightarrow> 0 \<le> a \<Longrightarrow> 0 \<le> c \<Longrightarrow> a * c \<le> b * d"
apply (rule mult_mono)
apply (fast intro: order_trans)+
done
end
class ordered_cancel_semiring = ordered_semiring + cancel_comm_monoid_add
begin
subclass semiring_0_cancel ..
lemma mult_nonneg_nonneg[simp]: "0 \<le> a \<Longrightarrow> 0 \<le> b \<Longrightarrow> 0 \<le> a * b"
using mult_left_mono [of 0 b a] by simp
lemma mult_nonneg_nonpos: "0 \<le> a \<Longrightarrow> b \<le> 0 \<Longrightarrow> a * b \<le> 0"
using mult_left_mono [of b 0 a] by simp
lemma mult_nonpos_nonneg: "a \<le> 0 \<Longrightarrow> 0 \<le> b \<Longrightarrow> a * b \<le> 0"
using mult_right_mono [of a 0 b] by simp
text {* Legacy - use @{text mult_nonpos_nonneg} *}
lemma mult_nonneg_nonpos2: "0 \<le> a \<Longrightarrow> b \<le> 0 \<Longrightarrow> b * a \<le> 0"
by (drule mult_right_mono [of b 0], auto)
lemma split_mult_neg_le: "(0 \<le> a & b \<le> 0) | (a \<le> 0 & 0 \<le> b) \<Longrightarrow> a * b \<le> 0"
by (auto simp add: mult_nonneg_nonpos mult_nonneg_nonpos2)
end
class linordered_semiring = ordered_semiring + linordered_cancel_ab_semigroup_add
begin
subclass ordered_cancel_semiring ..
subclass ordered_comm_monoid_add ..
lemma mult_left_less_imp_less:
"c * a < c * b \<Longrightarrow> 0 \<le> c \<Longrightarrow> a < b"
by (force simp add: mult_left_mono not_le [symmetric])
lemma mult_right_less_imp_less:
"a * c < b * c \<Longrightarrow> 0 \<le> c \<Longrightarrow> a < b"
by (force simp add: mult_right_mono not_le [symmetric])
end
class linordered_semiring_1 = linordered_semiring + semiring_1
begin
lemma convex_bound_le:
assumes "x \<le> a" "y \<le> a" "0 \<le> u" "0 \<le> v" "u + v = 1"
shows "u * x + v * y \<le> a"
proof-
from assms have "u * x + v * y \<le> u * a + v * a"
by (simp add: add_mono mult_left_mono)
thus ?thesis using assms unfolding distrib_right[symmetric] by simp
qed
end
class linordered_semiring_strict = semiring + comm_monoid_add + linordered_cancel_ab_semigroup_add +
assumes mult_strict_left_mono: "a < b \<Longrightarrow> 0 < c \<Longrightarrow> c * a < c * b"
assumes mult_strict_right_mono: "a < b \<Longrightarrow> 0 < c \<Longrightarrow> a * c < b * c"
begin
subclass semiring_0_cancel ..
subclass linordered_semiring
proof
fix a b c :: 'a
assume A: "a \<le> b" "0 \<le> c"
from A show "c * a \<le> c * b"
unfolding le_less
using mult_strict_left_mono by (cases "c = 0") auto
from A show "a * c \<le> b * c"
unfolding le_less
using mult_strict_right_mono by (cases "c = 0") auto
qed
lemma mult_left_le_imp_le:
"c * a \<le> c * b \<Longrightarrow> 0 < c \<Longrightarrow> a \<le> b"
by (force simp add: mult_strict_left_mono _not_less [symmetric])
lemma mult_right_le_imp_le:
"a * c \<le> b * c \<Longrightarrow> 0 < c \<Longrightarrow> a \<le> b"
by (force simp add: mult_strict_right_mono not_less [symmetric])
lemma mult_pos_pos[simp]: "0 < a \<Longrightarrow> 0 < b \<Longrightarrow> 0 < a * b"
using mult_strict_left_mono [of 0 b a] by simp
lemma mult_pos_neg: "0 < a \<Longrightarrow> b < 0 \<Longrightarrow> a * b < 0"
using mult_strict_left_mono [of b 0 a] by simp
lemma mult_neg_pos: "a < 0 \<Longrightarrow> 0 < b \<Longrightarrow> a * b < 0"
using mult_strict_right_mono [of a 0 b] by simp
text {* Legacy - use @{text mult_neg_pos} *}
lemma mult_pos_neg2: "0 < a \<Longrightarrow> b < 0 \<Longrightarrow> b * a < 0"
by (drule mult_strict_right_mono [of b 0], auto)
lemma zero_less_mult_pos:
"0 < a * b \<Longrightarrow> 0 < a \<Longrightarrow> 0 < b"
apply (cases "b\<le>0")
apply (auto simp add: le_less not_less)
apply (drule_tac mult_pos_neg [of a b])
apply (auto dest: less_not_sym)
done
lemma zero_less_mult_pos2:
"0 < b * a \<Longrightarrow> 0 < a \<Longrightarrow> 0 < b"
apply (cases "b\<le>0")
apply (auto simp add: le_less not_less)
apply (drule_tac mult_pos_neg2 [of a b])
apply (auto dest: less_not_sym)
done
text{*Strict monotonicity in both arguments*}
lemma mult_strict_mono:
assumes "a < b" and "c < d" and "0 < b" and "0 \<le> c"
shows "a * c < b * d"
using assms apply (cases "c=0")
apply (simp)
apply (erule mult_strict_right_mono [THEN less_trans])
apply (force simp add: le_less)
apply (erule mult_strict_left_mono, assumption)
done
text{*This weaker variant has more natural premises*}
lemma mult_strict_mono':
assumes "a < b" and "c < d" and "0 \<le> a" and "0 \<le> c"
shows "a * c < b * d"
by (rule mult_strict_mono) (insert assms, auto)
lemma mult_less_le_imp_less:
assumes "a < b" and "c \<le> d" and "0 \<le> a" and "0 < c"
shows "a * c < b * d"
using assms apply (subgoal_tac "a * c < b * c")
apply (erule less_le_trans)
apply (erule mult_left_mono)
apply simp
apply (erule mult_strict_right_mono)
apply assumption
done
lemma mult_le_less_imp_less:
assumes "a \<le> b" and "c < d" and "0 < a" and "0 \<le> c"
shows "a * c < b * d"
using assms apply (subgoal_tac "a * c \<le> b * c")
apply (erule le_less_trans)
apply (erule mult_strict_left_mono)
apply simp
apply (erule mult_right_mono)
apply simp
done
lemma mult_less_imp_less_left:
assumes less: "c * a < c * b" and nonneg: "0 \<le> c"
shows "a < b"
proof (rule ccontr)
assume "\<not> a < b"
hence "b \<le> a" by (simp add: linorder_not_less)
hence "c * b \<le> c * a" using nonneg by (rule mult_left_mono)
with this and less show False by (simp add: not_less [symmetric])
qed
lemma mult_less_imp_less_right:
assumes less: "a * c < b * c" and nonneg: "0 \<le> c"
shows "a < b"
proof (rule ccontr)
assume "\<not> a < b"
hence "b \<le> a" by (simp add: linorder_not_less)
hence "b * c \<le> a * c" using nonneg by (rule mult_right_mono)
with this and less show False by (simp add: not_less [symmetric])
qed
end
class linordered_semiring_1_strict = linordered_semiring_strict + semiring_1
begin
subclass linordered_semiring_1 ..
lemma convex_bound_lt:
assumes "x < a" "y < a" "0 \<le> u" "0 \<le> v" "u + v = 1"
shows "u * x + v * y < a"
proof -
from assms have "u * x + v * y < u * a + v * a"
by (cases "u = 0")
(auto intro!: add_less_le_mono mult_strict_left_mono mult_left_mono)
thus ?thesis using assms unfolding distrib_right[symmetric] by simp
qed
end
class ordered_comm_semiring = comm_semiring_0 + ordered_ab_semigroup_add +
assumes comm_mult_left_mono: "a \<le> b \<Longrightarrow> 0 \<le> c \<Longrightarrow> c * a \<le> c * b"
begin
subclass ordered_semiring
proof
fix a b c :: 'a
assume "a \<le> b" "0 \<le> c"
thus "c * a \<le> c * b" by (rule comm_mult_left_mono)
thus "a * c \<le> b * c" by (simp only: mult_commute)
qed
end
class ordered_cancel_comm_semiring = ordered_comm_semiring + cancel_comm_monoid_add
begin
subclass comm_semiring_0_cancel ..
subclass ordered_comm_semiring ..
subclass ordered_cancel_semiring ..
end
class linordered_comm_semiring_strict = comm_semiring_0 + linordered_cancel_ab_semigroup_add +
assumes comm_mult_strict_left_mono: "a < b \<Longrightarrow> 0 < c \<Longrightarrow> c * a < c * b"
begin
subclass linordered_semiring_strict
proof
fix a b c :: 'a
assume "a < b" "0 < c"
thus "c * a < c * b" by (rule comm_mult_strict_left_mono)
thus "a * c < b * c" by (simp only: mult_commute)
qed
subclass ordered_cancel_comm_semiring
proof
fix a b c :: 'a
assume "a \<le> b" "0 \<le> c"
thus "c * a \<le> c * b"
unfolding le_less
using mult_strict_left_mono by (cases "c = 0") auto
qed
end
class ordered_ring = ring + ordered_cancel_semiring
begin
subclass ordered_ab_group_add ..
lemma less_add_iff1:
"a * e + c < b * e + d \<longleftrightarrow> (a - b) * e + c < d"
by (simp add: algebra_simps)
lemma less_add_iff2:
"a * e + c < b * e + d \<longleftrightarrow> c < (b - a) * e + d"
by (simp add: algebra_simps)
lemma le_add_iff1:
"a * e + c \<le> b * e + d \<longleftrightarrow> (a - b) * e + c \<le> d"
by (simp add: algebra_simps)
lemma le_add_iff2:
"a * e + c \<le> b * e + d \<longleftrightarrow> c \<le> (b - a) * e + d"
by (simp add: algebra_simps)
lemma mult_left_mono_neg:
"b \<le> a \<Longrightarrow> c \<le> 0 \<Longrightarrow> c * a \<le> c * b"
apply (drule mult_left_mono [of _ _ "- c"])
apply simp_all
done
lemma mult_right_mono_neg:
"b \<le> a \<Longrightarrow> c \<le> 0 \<Longrightarrow> a * c \<le> b * c"
apply (drule mult_right_mono [of _ _ "- c"])
apply simp_all
done
lemma mult_nonpos_nonpos: "a \<le> 0 \<Longrightarrow> b \<le> 0 \<Longrightarrow> 0 \<le> a * b"
using mult_right_mono_neg [of a 0 b] by simp
lemma split_mult_pos_le:
"(0 \<le> a \<and> 0 \<le> b) \<or> (a \<le> 0 \<and> b \<le> 0) \<Longrightarrow> 0 \<le> a * b"
by (auto simp add: mult_nonpos_nonpos)
end
class linordered_ring = ring + linordered_semiring + linordered_ab_group_add + abs_if
begin
subclass ordered_ring ..
subclass ordered_ab_group_add_abs
proof
fix a b
show "\<bar>a + b\<bar> \<le> \<bar>a\<bar> + \<bar>b\<bar>"
by (auto simp add: abs_if not_le not_less algebra_simps simp del: add.commute dest: add_neg_neg add_nonneg_nonneg)
qed (auto simp add: abs_if)
lemma zero_le_square [simp]: "0 \<le> a * a"
using linear [of 0 a]
by (auto simp add: mult_nonpos_nonpos)
lemma not_square_less_zero [simp]: "\<not> (a * a < 0)"
by (simp add: not_less)
end
(* The "strict" suffix can be seen as describing the combination of linordered_ring and no_zero_divisors.
Basically, linordered_ring + no_zero_divisors = linordered_ring_strict.
*)
class linordered_ring_strict = ring + linordered_semiring_strict
+ ordered_ab_group_add + abs_if
begin
subclass linordered_ring ..
lemma mult_strict_left_mono_neg: "b < a \<Longrightarrow> c < 0 \<Longrightarrow> c * a < c * b"
using mult_strict_left_mono [of b a "- c"] by simp
lemma mult_strict_right_mono_neg: "b < a \<Longrightarrow> c < 0 \<Longrightarrow> a * c < b * c"
using mult_strict_right_mono [of b a "- c"] by simp
lemma mult_neg_neg: "a < 0 \<Longrightarrow> b < 0 \<Longrightarrow> 0 < a * b"
using mult_strict_right_mono_neg [of a 0 b] by simp
subclass ring_no_zero_divisors
proof
fix a b
assume "a \<noteq> 0" then have A: "a < 0 \<or> 0 < a" by (simp add: neq_iff)
assume "b \<noteq> 0" then have B: "b < 0 \<or> 0 < b" by (simp add: neq_iff)
have "a * b < 0 \<or> 0 < a * b"
proof (cases "a < 0")
case True note A' = this
show ?thesis proof (cases "b < 0")
case True with A'
show ?thesis by (auto dest: mult_neg_neg)
next
case False with B have "0 < b" by auto
with A' show ?thesis by (auto dest: mult_strict_right_mono)
qed
next
case False with A have A': "0 < a" by auto
show ?thesis proof (cases "b < 0")
case True with A'
show ?thesis by (auto dest: mult_strict_right_mono_neg)
next
case False with B have "0 < b" by auto
with A' show ?thesis by auto
qed
qed
then show "a * b \<noteq> 0" by (simp add: neq_iff)
qed
lemma zero_less_mult_iff: "0 < a * b \<longleftrightarrow> 0 < a \<and> 0 < b \<or> a < 0 \<and> b < 0"
by (cases a 0 b 0 rule: linorder_cases[case_product linorder_cases])
(auto simp add: mult_neg_neg not_less le_less dest: zero_less_mult_pos zero_less_mult_pos2)
lemma zero_le_mult_iff: "0 \<le> a * b \<longleftrightarrow> 0 \<le> a \<and> 0 \<le> b \<or> a \<le> 0 \<and> b \<le> 0"
by (auto simp add: eq_commute [of 0] le_less not_less zero_less_mult_iff)
lemma mult_less_0_iff:
"a * b < 0 \<longleftrightarrow> 0 < a \<and> b < 0 \<or> a < 0 \<and> 0 < b"
apply (insert zero_less_mult_iff [of "-a" b])
apply force
done
lemma mult_le_0_iff:
"a * b \<le> 0 \<longleftrightarrow> 0 \<le> a \<and> b \<le> 0 \<or> a \<le> 0 \<and> 0 \<le> b"
apply (insert zero_le_mult_iff [of "-a" b])
apply force
done
text{*Cancellation laws for @{term "c*a < c*b"} and @{term "a*c < b*c"},
also with the relations @{text "\<le>"} and equality.*}
text{*These ``disjunction'' versions produce two cases when the comparison is
an assumption, but effectively four when the comparison is a goal.*}
lemma mult_less_cancel_right_disj:
"a * c < b * c \<longleftrightarrow> 0 < c \<and> a < b \<or> c < 0 \<and> b < a"
apply (cases "c = 0")
apply (auto simp add: neq_iff mult_strict_right_mono
mult_strict_right_mono_neg)
apply (auto simp add: not_less
not_le [symmetric, of "a*c"]
not_le [symmetric, of a])
apply (erule_tac [!] notE)
apply (auto simp add: less_imp_le mult_right_mono
mult_right_mono_neg)
done
lemma mult_less_cancel_left_disj:
"c * a < c * b \<longleftrightarrow> 0 < c \<and> a < b \<or> c < 0 \<and> b < a"
apply (cases "c = 0")
apply (auto simp add: neq_iff mult_strict_left_mono
mult_strict_left_mono_neg)
apply (auto simp add: not_less
not_le [symmetric, of "c*a"]
not_le [symmetric, of a])
apply (erule_tac [!] notE)
apply (auto simp add: less_imp_le mult_left_mono
mult_left_mono_neg)
done
text{*The ``conjunction of implication'' lemmas produce two cases when the
comparison is a goal, but give four when the comparison is an assumption.*}
lemma mult_less_cancel_right:
"a * c < b * c \<longleftrightarrow> (0 \<le> c \<longrightarrow> a < b) \<and> (c \<le> 0 \<longrightarrow> b < a)"
using mult_less_cancel_right_disj [of a c b] by auto
lemma mult_less_cancel_left:
"c * a < c * b \<longleftrightarrow> (0 \<le> c \<longrightarrow> a < b) \<and> (c \<le> 0 \<longrightarrow> b < a)"
using mult_less_cancel_left_disj [of c a b] by auto
lemma mult_le_cancel_right:
"a * c \<le> b * c \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> a)"
by (simp add: not_less [symmetric] mult_less_cancel_right_disj)
lemma mult_le_cancel_left:
"c * a \<le> c * b \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> a)"
by (simp add: not_less [symmetric] mult_less_cancel_left_disj)
lemma mult_le_cancel_left_pos:
"0 < c \<Longrightarrow> c * a \<le> c * b \<longleftrightarrow> a \<le> b"
by (auto simp: mult_le_cancel_left)
lemma mult_le_cancel_left_neg:
"c < 0 \<Longrightarrow> c * a \<le> c * b \<longleftrightarrow> b \<le> a"
by (auto simp: mult_le_cancel_left)
lemma mult_less_cancel_left_pos:
"0 < c \<Longrightarrow> c * a < c * b \<longleftrightarrow> a < b"
by (auto simp: mult_less_cancel_left)
lemma mult_less_cancel_left_neg:
"c < 0 \<Longrightarrow> c * a < c * b \<longleftrightarrow> b < a"
by (auto simp: mult_less_cancel_left)
end
lemmas mult_sign_intros =
mult_nonneg_nonneg mult_nonneg_nonpos
mult_nonpos_nonneg mult_nonpos_nonpos
mult_pos_pos mult_pos_neg
mult_neg_pos mult_neg_neg
class ordered_comm_ring = comm_ring + ordered_comm_semiring
begin
subclass ordered_ring ..
subclass ordered_cancel_comm_semiring ..
end
class linordered_semidom = comm_semiring_1_cancel + linordered_comm_semiring_strict +
(*previously linordered_semiring*)
assumes zero_less_one [simp]: "0 < 1"
begin
lemma pos_add_strict:
shows "0 < a \<Longrightarrow> b < c \<Longrightarrow> b < a + c"
using add_strict_mono [of 0 a b c] by simp
lemma zero_le_one [simp]: "0 \<le> 1"
by (rule zero_less_one [THEN less_imp_le])
lemma not_one_le_zero [simp]: "\<not> 1 \<le> 0"
by (simp add: not_le)
lemma not_one_less_zero [simp]: "\<not> 1 < 0"
by (simp add: not_less)
lemma less_1_mult:
assumes "1 < m" and "1 < n"
shows "1 < m * n"
using assms mult_strict_mono [of 1 m 1 n]
by (simp add: less_trans [OF zero_less_one])
end
class linordered_idom = comm_ring_1 +
linordered_comm_semiring_strict + ordered_ab_group_add +
abs_if + sgn_if
(*previously linordered_ring*)
begin
subclass linordered_semiring_1_strict ..
subclass linordered_ring_strict ..
subclass ordered_comm_ring ..
subclass idom ..
subclass linordered_semidom
proof
have "0 \<le> 1 * 1" by (rule zero_le_square)
thus "0 < 1" by (simp add: le_less)
qed
lemma linorder_neqE_linordered_idom:
assumes "x \<noteq> y" obtains "x < y" | "y < x"
using assms by (rule neqE)
text {* These cancellation simprules also produce two cases when the comparison is a goal. *}
lemma mult_le_cancel_right1:
"c \<le> b * c \<longleftrightarrow> (0 < c \<longrightarrow> 1 \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> 1)"
by (insert mult_le_cancel_right [of 1 c b], simp)
lemma mult_le_cancel_right2:
"a * c \<le> c \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> 1) \<and> (c < 0 \<longrightarrow> 1 \<le> a)"
by (insert mult_le_cancel_right [of a c 1], simp)
lemma mult_le_cancel_left1:
"c \<le> c * b \<longleftrightarrow> (0 < c \<longrightarrow> 1 \<le> b) \<and> (c < 0 \<longrightarrow> b \<le> 1)"
by (insert mult_le_cancel_left [of c 1 b], simp)
lemma mult_le_cancel_left2:
"c * a \<le> c \<longleftrightarrow> (0 < c \<longrightarrow> a \<le> 1) \<and> (c < 0 \<longrightarrow> 1 \<le> a)"
by (insert mult_le_cancel_left [of c a 1], simp)
lemma mult_less_cancel_right1:
"c < b * c \<longleftrightarrow> (0 \<le> c \<longrightarrow> 1 < b) \<and> (c \<le> 0 \<longrightarrow> b < 1)"
by (insert mult_less_cancel_right [of 1 c b], simp)
lemma mult_less_cancel_right2:
"a * c < c \<longleftrightarrow> (0 \<le> c \<longrightarrow> a < 1) \<and> (c \<le> 0 \<longrightarrow> 1 < a)"
by (insert mult_less_cancel_right [of a c 1], simp)
lemma mult_less_cancel_left1:
"c < c * b \<longleftrightarrow> (0 \<le> c \<longrightarrow> 1 < b) \<and> (c \<le> 0 \<longrightarrow> b < 1)"
by (insert mult_less_cancel_left [of c 1 b], simp)
lemma mult_less_cancel_left2:
"c * a < c \<longleftrightarrow> (0 \<le> c \<longrightarrow> a < 1) \<and> (c \<le> 0 \<longrightarrow> 1 < a)"
by (insert mult_less_cancel_left [of c a 1], simp)
lemma sgn_sgn [simp]:
"sgn (sgn a) = sgn a"
unfolding sgn_if by simp
lemma sgn_0_0:
"sgn a = 0 \<longleftrightarrow> a = 0"
unfolding sgn_if by simp
lemma sgn_1_pos:
"sgn a = 1 \<longleftrightarrow> a > 0"
unfolding sgn_if by simp
lemma sgn_1_neg:
"sgn a = - 1 \<longleftrightarrow> a < 0"
unfolding sgn_if by auto
lemma sgn_pos [simp]:
"0 < a \<Longrightarrow> sgn a = 1"
unfolding sgn_1_pos .
lemma sgn_neg [simp]:
"a < 0 \<Longrightarrow> sgn a = - 1"
unfolding sgn_1_neg .
lemma sgn_times:
"sgn (a * b) = sgn a * sgn b"
by (auto simp add: sgn_if zero_less_mult_iff)
lemma abs_sgn: "\<bar>k\<bar> = k * sgn k"
unfolding sgn_if abs_if by auto
lemma sgn_greater [simp]:
"0 < sgn a \<longleftrightarrow> 0 < a"
unfolding sgn_if by auto
lemma sgn_less [simp]:
"sgn a < 0 \<longleftrightarrow> a < 0"
unfolding sgn_if by auto
lemma abs_dvd_iff [simp]: "\<bar>m\<bar> dvd k \<longleftrightarrow> m dvd k"
by (simp add: abs_if)
lemma dvd_abs_iff [simp]: "m dvd \<bar>k\<bar> \<longleftrightarrow> m dvd k"
by (simp add: abs_if)
lemma dvd_if_abs_eq:
"\<bar>l\<bar> = \<bar>k\<bar> \<Longrightarrow> l dvd k"
by(subst abs_dvd_iff[symmetric]) simp
text {* The following lemmas can be proven in more general structures, but
are dangerous as simp rules in absence of @{thm neg_equal_zero},
@{thm neg_less_pos}, @{thm neg_less_eq_nonneg}. *}
lemma equation_minus_iff_1 [simp, no_atp]:
"1 = - a \<longleftrightarrow> a = - 1"
by (fact equation_minus_iff)
lemma minus_equation_iff_1 [simp, no_atp]:
"- a = 1 \<longleftrightarrow> a = - 1"
by (subst minus_equation_iff, auto)
lemma le_minus_iff_1 [simp, no_atp]:
"1 \<le> - b \<longleftrightarrow> b \<le> - 1"
by (fact le_minus_iff)
lemma minus_le_iff_1 [simp, no_atp]:
"- a \<le> 1 \<longleftrightarrow> - 1 \<le> a"
by (fact minus_le_iff)
lemma less_minus_iff_1 [simp, no_atp]:
"1 < - b \<longleftrightarrow> b < - 1"
by (fact less_minus_iff)
lemma minus_less_iff_1 [simp, no_atp]:
"- a < 1 \<longleftrightarrow> - 1 < a"
by (fact minus_less_iff)
end
text {* Simprules for comparisons where common factors can be cancelled. *}
lemmas mult_compare_simps =
mult_le_cancel_right mult_le_cancel_left
mult_le_cancel_right1 mult_le_cancel_right2
mult_le_cancel_left1 mult_le_cancel_left2
mult_less_cancel_right mult_less_cancel_left
mult_less_cancel_right1 mult_less_cancel_right2
mult_less_cancel_left1 mult_less_cancel_left2
mult_cancel_right mult_cancel_left
mult_cancel_right1 mult_cancel_right2
mult_cancel_left1 mult_cancel_left2
text {* Reasoning about inequalities with division *}
context linordered_semidom
begin
lemma less_add_one: "a < a + 1"
proof -
have "a + 0 < a + 1"
by (blast intro: zero_less_one add_strict_left_mono)
thus ?thesis by simp
qed
lemma zero_less_two: "0 < 1 + 1"
by (blast intro: less_trans zero_less_one less_add_one)
end
context linordered_idom
begin
lemma mult_right_le_one_le:
"0 \<le> x \<Longrightarrow> 0 \<le> y \<Longrightarrow> y \<le> 1 \<Longrightarrow> x * y \<le> x"
by (auto simp add: mult_le_cancel_left2)
lemma mult_left_le_one_le:
"0 \<le> x \<Longrightarrow> 0 \<le> y \<Longrightarrow> y \<le> 1 \<Longrightarrow> y * x \<le> x"
by (auto simp add: mult_le_cancel_right2)
end
text {* Absolute Value *}
context linordered_idom
begin
lemma mult_sgn_abs:
"sgn x * \<bar>x\<bar> = x"
unfolding abs_if sgn_if by auto
lemma abs_one [simp]:
"\<bar>1\<bar> = 1"
by (simp add: abs_if)
end
class ordered_ring_abs = ordered_ring + ordered_ab_group_add_abs +
assumes abs_eq_mult:
"(0 \<le> a \<or> a \<le> 0) \<and> (0 \<le> b \<or> b \<le> 0) \<Longrightarrow> \<bar>a * b\<bar> = \<bar>a\<bar> * \<bar>b\<bar>"
context linordered_idom
begin
subclass ordered_ring_abs proof
qed (auto simp add: abs_if not_less mult_less_0_iff)
lemma abs_mult:
"\<bar>a * b\<bar> = \<bar>a\<bar> * \<bar>b\<bar>"
by (rule abs_eq_mult) auto
lemma abs_mult_self:
"\<bar>a\<bar> * \<bar>a\<bar> = a * a"
by (simp add: abs_if)
lemma abs_mult_less:
"\<bar>a\<bar> < c \<Longrightarrow> \<bar>b\<bar> < d \<Longrightarrow> \<bar>a\<bar> * \<bar>b\<bar> < c * d"
proof -
assume ac: "\<bar>a\<bar> < c"
hence cpos: "0<c" by (blast intro: le_less_trans abs_ge_zero)
assume "\<bar>b\<bar> < d"
thus ?thesis by (simp add: ac cpos mult_strict_mono)
qed
lemma abs_less_iff:
"\<bar>a\<bar> < b \<longleftrightarrow> a < b \<and> - a < b"
by (simp add: less_le abs_le_iff) (auto simp add: abs_if)
lemma abs_mult_pos:
"0 \<le> x \<Longrightarrow> \<bar>y\<bar> * x = \<bar>y * x\<bar>"
by (simp add: abs_mult)
lemma abs_diff_less_iff:
"\<bar>x - a\<bar> < r \<longleftrightarrow> a - r < x \<and> x < a + r"
by (auto simp add: diff_less_eq ac_simps abs_less_iff)
end
code_identifier
code_module Rings \<rightharpoonup> (SML) Arith and (OCaml) Arith and (Haskell) Arith
end