author | wenzelm |
Mon, 07 Feb 2000 18:38:51 +0100 | |
changeset 8203 | 2fcc6017cb72 |
parent 7978 | 1b99ee57d131 |
child 8703 | 816d8f6513be |
permissions | -rw-r--r-- |
7917 | 1 |
(* Title: HOL/Real/HahnBanach/VectorSpace.thy |
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ID: $Id$ |
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Author: Gertrud Bauer, TU Munich |
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*) |
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header {* Vector spaces *}; |
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theory VectorSpace = Bounds + Aux:; |
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subsection {* Signature *}; |
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text {* For the definition of real vector spaces a type $\alpha$ |
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of the sort $\{ \idt{plus}, \idt{minus}\}$ is considered, on which a |
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real scalar multiplication $\mult$, and a zero |
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element $\zero$ is defined. *}; |
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consts |
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prod :: "[real, 'a] => 'a" (infixr "<*>" 70) |
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zero :: 'a ("<0>"); |
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syntax (symbols) |
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prod :: "[real, 'a] => 'a" (infixr "\<prod>" 70) |
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zero :: 'a ("\<zero>"); |
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(* text {* The unary and binary minus can be considered as |
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abbreviations: *}; |
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*) |
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(*** |
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constdefs |
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negate :: "'a => 'a" ("- _" [100] 100) |
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"- x == (- 1r) <*> x" |
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diff :: "'a => 'a => 'a" (infixl "-" 68) |
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"x - y == x + - y"; |
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***) |
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subsection {* Vector space laws *}; |
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text {* A \emph{vector space} is a non-empty set $V$ of elements from |
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$\alpha$ with the following vector space laws: The set $V$ is closed |
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under addition and scalar multiplication, addition is associative |
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and commutative; $\minus x$ is the inverse of $x$ w.~r.~t.~addition |
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and $\zero$ is the neutral element of addition. Addition and |
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multiplication are distributive; scalar multiplication is |
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associative and the real number $1$ is the neutral element of scalar |
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multiplication. |
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*}; |
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constdefs |
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is_vectorspace :: "('a::{plus,minus}) set => bool" |
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"is_vectorspace V == V ~= {} |
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& (ALL x:V. ALL y:V. ALL z:V. ALL a b. |
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x + y : V |
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& a <*> x : V |
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& (x + y) + z = x + (y + z) |
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& x + y = y + x |
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& x - x = <0> |
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& <0> + x = x |
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& a <*> (x + y) = a <*> x + a <*> y |
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& (a + b) <*> x = a <*> x + b <*> x |
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& (a * b) <*> x = a <*> b <*> x |
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& 1r <*> x = x |
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& - x = (- 1r) <*> x |
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& x - y = x + - y)"; |
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text_raw {* \medskip *}; |
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text {* The corresponding introduction rule is:*}; |
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lemma vsI [intro]: |
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"[| <0>:V; |
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ALL x:V. ALL y:V. x + y : V; |
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ALL x:V. ALL a. a <*> x : V; |
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ALL x:V. ALL y:V. ALL z:V. (x + y) + z = x + (y + z); |
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ALL x:V. ALL y:V. x + y = y + x; |
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ALL x:V. x - x = <0>; |
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ALL x:V. <0> + x = x; |
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ALL x:V. ALL y:V. ALL a. a <*> (x + y) = a <*> x + a <*> y; |
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ALL x:V. ALL a b. (a + b) <*> x = a <*> x + b <*> x; |
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ALL x:V. ALL a b. (a * b) <*> x = a <*> b <*> x; |
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ALL x:V. 1r <*> x = x; |
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ALL x:V. - x = (- 1r) <*> x; |
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ALL x:V. ALL y:V. x - y = x + - y |] ==> is_vectorspace V"; |
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proof (unfold is_vectorspace_def, intro conjI ballI allI); |
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fix x y z; |
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assume "x:V" "y:V" "z:V" |
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"ALL x:V. ALL y:V. ALL z:V. x + y + z = x + (y + z)"; |
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thus "x + y + z = x + (y + z)"; by (elim bspec[elimify]); |
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qed force+; |
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text_raw {* \medskip *}; |
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text {* The corresponding destruction rules are: *}; |
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lemma negate_eq1: |
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"[| is_vectorspace V; x:V |] ==> - x = (- 1r) <*> x"; |
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by (unfold is_vectorspace_def) simp; |
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lemma diff_eq1: |
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"[| is_vectorspace V; x:V; y:V |] ==> x - y = x + - y"; |
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by (unfold is_vectorspace_def) simp; |
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lemma negate_eq2: |
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"[| is_vectorspace V; x:V |] ==> (- 1r) <*> x = - x"; |
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by (unfold is_vectorspace_def) simp; |
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lemma diff_eq2: |
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"[| is_vectorspace V; x:V; y:V |] ==> x + - y = x - y"; |
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by (unfold is_vectorspace_def) simp; |
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lemma vs_not_empty [intro??]: "is_vectorspace V ==> (V ~= {})"; |
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by (unfold is_vectorspace_def) simp; |
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lemma vs_add_closed [simp, intro??]: |
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"[| is_vectorspace V; x:V; y:V |] ==> x + y : V"; |
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by (unfold is_vectorspace_def) simp; |
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lemma vs_mult_closed [simp, intro??]: |
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"[| is_vectorspace V; x:V |] ==> a <*> x : V"; |
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by (unfold is_vectorspace_def) simp; |
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lemma vs_diff_closed [simp, intro??]: |
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"[| is_vectorspace V; x:V; y:V |] ==> x - y : V"; |
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by (simp add: diff_eq1 negate_eq1); |
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lemma vs_neg_closed [simp, intro??]: |
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"[| is_vectorspace V; x:V |] ==> - x : V"; |
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by (simp add: negate_eq1); |
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lemma vs_add_assoc [simp]: |
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"[| is_vectorspace V; x:V; y:V; z:V |] |
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==> (x + y) + z = x + (y + z)"; |
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by (unfold is_vectorspace_def) fast; |
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lemma vs_add_commute [simp]: |
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"[| is_vectorspace V; x:V; y:V |] ==> y + x = x + y"; |
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by (unfold is_vectorspace_def) simp; |
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lemma vs_add_left_commute [simp]: |
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"[| is_vectorspace V; x:V; y:V; z:V |] |
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==> x + (y + z) = y + (x + z)"; |
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proof -; |
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assume "is_vectorspace V" "x:V" "y:V" "z:V"; |
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hence "x + (y + z) = (x + y) + z"; |
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by (simp only: vs_add_assoc); |
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also; have "... = (y + x) + z"; by (simp! only: vs_add_commute); |
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also; have "... = y + (x + z)"; by (simp! only: vs_add_assoc); |
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finally; show ?thesis; .; |
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qed; |
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theorems vs_add_ac = vs_add_assoc vs_add_commute vs_add_left_commute; |
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lemma vs_diff_self [simp]: |
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"[| is_vectorspace V; x:V |] ==> x - x = <0>"; |
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by (unfold is_vectorspace_def) simp; |
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text {* The existence of the zero element of a vector space |
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follows from the non-emptiness of carrier set. *}; |
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lemma zero_in_vs [simp, intro]: "is_vectorspace V ==> <0>:V"; |
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proof -; |
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assume "is_vectorspace V"; |
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have "V ~= {}"; ..; |
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hence "EX x. x:V"; by force; |
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thus ?thesis; |
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proof; |
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fix x; assume "x:V"; |
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have "<0> = x - x"; by (simp!); |
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also; have "... : V"; by (simp! only: vs_diff_closed); |
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finally; show ?thesis; .; |
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qed; |
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qed; |
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lemma vs_add_zero_left [simp]: |
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"[| is_vectorspace V; x:V |] ==> <0> + x = x"; |
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by (unfold is_vectorspace_def) simp; |
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lemma vs_add_zero_right [simp]: |
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"[| is_vectorspace V; x:V |] ==> x + <0> = x"; |
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proof -; |
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assume "is_vectorspace V" "x:V"; |
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hence "x + <0> = <0> + x"; by simp; |
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also; have "... = x"; by (simp!); |
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finally; show ?thesis; .; |
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qed; |
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lemma vs_add_mult_distrib1: |
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"[| is_vectorspace V; x:V; y:V |] |
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==> a <*> (x + y) = a <*> x + a <*> y"; |
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by (unfold is_vectorspace_def) simp; |
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lemma vs_add_mult_distrib2: |
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"[| is_vectorspace V; x:V |] |
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==> (a + b) <*> x = a <*> x + b <*> x"; |
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by (unfold is_vectorspace_def) simp; |
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lemma vs_mult_assoc: |
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"[| is_vectorspace V; x:V |] ==> (a * b) <*> x = a <*> (b <*> x)"; |
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by (unfold is_vectorspace_def) simp; |
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lemma vs_mult_assoc2 [simp]: |
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"[| is_vectorspace V; x:V |] ==> a <*> b <*> x = (a * b) <*> x"; |
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by (simp only: vs_mult_assoc); |
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lemma vs_mult_1 [simp]: |
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"[| is_vectorspace V; x:V |] ==> 1r <*> x = x"; |
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by (unfold is_vectorspace_def) simp; |
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lemma vs_diff_mult_distrib1: |
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"[| is_vectorspace V; x:V; y:V |] |
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==> a <*> (x - y) = a <*> x - a <*> y"; |
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by (simp add: diff_eq1 negate_eq1 vs_add_mult_distrib1); |
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lemma vs_diff_mult_distrib2: |
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"[| is_vectorspace V; x:V |] |
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==> (a - b) <*> x = a <*> x - (b <*> x)"; |
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proof -; |
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assume "is_vectorspace V" "x:V"; |
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have " (a - b) <*> x = (a + - b ) <*> x"; |
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by (unfold real_diff_def, simp); |
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also; have "... = a <*> x + (- b) <*> x"; |
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by (rule vs_add_mult_distrib2); |
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also; have "... = a <*> x + - (b <*> x)"; |
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by (simp! add: negate_eq1); |
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also; have "... = a <*> x - (b <*> x)"; |
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by (simp! add: diff_eq1); |
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finally; show ?thesis; .; |
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qed; |
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(*text_raw {* \paragraph {Further derived laws.} *};*) |
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text_raw {* \medskip *}; |
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text{* Further derived laws: *}; |
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lemma vs_mult_zero_left [simp]: |
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"[| is_vectorspace V; x:V |] ==> 0r <*> x = <0>"; |
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proof -; |
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assume "is_vectorspace V" "x:V"; |
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have "0r <*> x = (1r - 1r) <*> x"; by (simp only: real_diff_self); |
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also; have "... = (1r + - 1r) <*> x"; by simp; |
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also; have "... = 1r <*> x + (- 1r) <*> x"; |
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by (rule vs_add_mult_distrib2); |
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also; have "... = x + (- 1r) <*> x"; by (simp!); |
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also; have "... = x + - x"; by (simp! add: negate_eq2);; |
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also; have "... = x - x"; by (simp! add: diff_eq2); |
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also; have "... = <0>"; by (simp!); |
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finally; show ?thesis; .; |
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qed; |
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lemma vs_mult_zero_right [simp]: |
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"[| is_vectorspace (V:: 'a::{plus, minus} set) |] |
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==> a <*> <0> = (<0>::'a)"; |
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proof -; |
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assume "is_vectorspace V"; |
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have "a <*> <0> = a <*> (<0> - (<0>::'a))"; by (simp!); |
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also; have "... = a <*> <0> - a <*> <0>"; |
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by (rule vs_diff_mult_distrib1) (simp!)+; |
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also; have "... = <0>"; by (simp!); |
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finally; show ?thesis; .; |
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qed; |
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lemma vs_minus_mult_cancel [simp]: |
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"[| is_vectorspace V; x:V |] ==> (- a) <*> - x = a <*> x"; |
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by (simp add: negate_eq1); |
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lemma vs_add_minus_left_eq_diff: |
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"[| is_vectorspace V; x:V; y:V |] ==> - x + y = y - x"; |
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proof -; |
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assume "is_vectorspace V" "x:V" "y:V"; |
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have "- x + y = y + - x"; |
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by (simp! add: vs_add_commute [RS sym, of V "- x"]); |
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also; have "... = y - x"; by (simp! add: diff_eq1); |
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finally; show ?thesis; .; |
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qed; |
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lemma vs_add_minus [simp]: |
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"[| is_vectorspace V; x:V |] ==> x + - x = <0>"; |
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by (simp! add: diff_eq2); |
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lemma vs_add_minus_left [simp]: |
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"[| is_vectorspace V; x:V |] ==> - x + x = <0>"; |
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by (simp! add: diff_eq2); |
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lemma vs_minus_minus [simp]: |
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"[| is_vectorspace V; x:V |] ==> - (- x) = x"; |
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by (simp add: negate_eq1); |
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lemma vs_minus_zero [simp]: |
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"is_vectorspace (V::'a::{minus, plus} set) ==> - (<0>::'a) = <0>"; |
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by (simp add: negate_eq1); |
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lemma vs_minus_zero_iff [simp]: |
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"[| is_vectorspace V; x:V |] ==> (- x = <0>) = (x = <0>)" |
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(concl is "?L = ?R"); |
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proof -; |
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assume "is_vectorspace V" "x:V"; |
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show "?L = ?R"; |
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proof; |
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have "x = - (- x)"; by (rule vs_minus_minus [RS sym]); |
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also; assume ?L; |
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also; have "- ... = <0>"; by (rule vs_minus_zero); |
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finally; show ?R; .; |
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qed (simp!); |
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qed; |
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lemma vs_add_minus_cancel [simp]: |
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"[| is_vectorspace V; x:V; y:V |] ==> x + (- x + y) = y"; |
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by (simp add: vs_add_assoc [RS sym] del: vs_add_commute); |
306 |
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lemma vs_minus_add_cancel [simp]: |
|
7978 | 308 |
"[| is_vectorspace V; x:V; y:V |] ==> - x + (x + y) = y"; |
7917 | 309 |
by (simp add: vs_add_assoc [RS sym] del: vs_add_commute); |
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lemma vs_minus_add_distrib [simp]: |
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"[| is_vectorspace V; x:V; y:V |] |
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==> - (x + y) = - x + - y"; |
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by (simp add: negate_eq1 vs_add_mult_distrib1); |
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lemma vs_diff_zero [simp]: |
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"[| is_vectorspace V; x:V |] ==> x - <0> = x"; |
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by (simp add: diff_eq1); |
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lemma vs_diff_zero_right [simp]: |
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"[| is_vectorspace V; x:V |] ==> <0> - x = - x"; |
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by (simp add:diff_eq1); |
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323 |
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324 |
lemma vs_add_left_cancel: |
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7978 | 325 |
"[| is_vectorspace V; x:V; y:V; z:V |] |
7917 | 326 |
==> (x + y = x + z) = (y = z)" |
327 |
(concl is "?L = ?R"); |
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328 |
proof; |
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329 |
assume "is_vectorspace V" "x:V" "y:V" "z:V"; |
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have "y = <0> + y"; by (simp!); |
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also; have "... = - x + x + y"; by (simp!); |
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also; have "... = - x + (x + y)"; |
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by (simp! only: vs_add_assoc vs_neg_closed); |
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also; assume ?L; |
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also; have "- x + ... = - x + x + z"; |
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by (rule vs_add_assoc [RS sym]) (simp!)+; |
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also; have "... = z"; by (simp!); |
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7978 | 338 |
finally; show ?R; .; |
7917 | 339 |
qed force; |
340 |
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lemma vs_add_right_cancel: |
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"[| is_vectorspace V; x:V; y:V; z:V |] |
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==> (y + x = z + x) = (y = z)"; |
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by (simp only: vs_add_commute vs_add_left_cancel); |
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lemma vs_add_assoc_cong: |
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"[| is_vectorspace V; x:V; y:V; x':V; y':V; z:V |] |
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==> x + y = x' + y' ==> x + (y + z) = x' + (y' + z)"; |
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by (simp only: vs_add_assoc [RS sym]); |
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351 |
lemma vs_mult_left_commute: |
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352 |
"[| is_vectorspace V; x:V; y:V; z:V |] |
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==> x <*> y <*> z = y <*> x <*> z"; |
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by (simp add: real_mult_commute); |
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356 |
lemma vs_mult_zero_uniq : |
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357 |
"[| is_vectorspace V; x:V; a <*> x = <0>; x ~= <0> |] ==> a = 0r"; |
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358 |
proof (rule classical); |
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359 |
assume "is_vectorspace V" "x:V" "a <*> x = <0>" "x ~= <0>"; |
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360 |
assume "a ~= 0r"; |
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have "x = (rinv a * a) <*> x"; by (simp!); |
|
362 |
also; have "... = rinv a <*> (a <*> x)"; by (rule vs_mult_assoc); |
|
363 |
also; have "... = rinv a <*> <0>"; by (simp!); |
|
364 |
also; have "... = <0>"; by (simp!); |
|
365 |
finally; have "x = <0>"; .; |
|
366 |
thus "a = 0r"; by contradiction; |
|
367 |
qed; |
|
368 |
||
369 |
lemma vs_mult_left_cancel: |
|
370 |
"[| is_vectorspace V; x:V; y:V; a ~= 0r |] ==> |
|
371 |
(a <*> x = a <*> y) = (x = y)" |
|
372 |
(concl is "?L = ?R"); |
|
373 |
proof; |
|
374 |
assume "is_vectorspace V" "x:V" "y:V" "a ~= 0r"; |
|
375 |
have "x = 1r <*> x"; by (simp!); |
|
376 |
also; have "... = (rinv a * a) <*> x"; by (simp!); |
|
377 |
also; have "... = rinv a <*> (a <*> x)"; |
|
378 |
by (simp! only: vs_mult_assoc); |
|
379 |
also; assume ?L; |
|
380 |
also; have "rinv a <*> ... = y"; by (simp!); |
|
7978 | 381 |
finally; show ?R; .; |
7917 | 382 |
qed simp; |
383 |
||
384 |
lemma vs_mult_right_cancel: (*** forward ***) |
|
385 |
"[| is_vectorspace V; x:V; x ~= <0> |] |
|
386 |
==> (a <*> x = b <*> x) = (a = b)" (concl is "?L = ?R"); |
|
387 |
proof; |
|
388 |
assume "is_vectorspace V" "x:V" "x ~= <0>"; |
|
389 |
have "(a - b) <*> x = a <*> x - b <*> x"; |
|
390 |
by (simp! add: vs_diff_mult_distrib2); |
|
391 |
also; assume ?L; hence "a <*> x - b <*> x = <0>"; by (simp!); |
|
392 |
finally; have "(a - b) <*> x = <0>"; .; |
|
393 |
hence "a - b = 0r"; by (simp! add: vs_mult_zero_uniq); |
|
394 |
thus "a = b"; by (rule real_add_minus_eq); |
|
395 |
qed simp; (*** |
|
396 |
||
397 |
backward : |
|
398 |
lemma vs_mult_right_cancel: |
|
399 |
"[| is_vectorspace V; x:V; x ~= <0> |] ==> |
|
400 |
(a <*> x = b <*> x) = (a = b)" |
|
401 |
(concl is "?L = ?R"); |
|
402 |
proof; |
|
403 |
assume "is_vectorspace V" "x:V" "x ~= <0>"; |
|
404 |
assume l: ?L; |
|
405 |
show "a = b"; |
|
406 |
proof (rule real_add_minus_eq); |
|
407 |
show "a - b = 0r"; |
|
408 |
proof (rule vs_mult_zero_uniq); |
|
409 |
have "(a - b) <*> x = a <*> x - b <*> x"; |
|
410 |
by (simp! add: vs_diff_mult_distrib2); |
|
411 |
also; from l; have "a <*> x - b <*> x = <0>"; by (simp!); |
|
412 |
finally; show "(a - b) <*> x = <0>"; .; |
|
413 |
qed; |
|
414 |
qed; |
|
415 |
next; |
|
416 |
assume ?R; |
|
417 |
thus ?L; by simp; |
|
418 |
qed; |
|
419 |
**) |
|
420 |
||
421 |
lemma vs_eq_diff_eq: |
|
422 |
"[| is_vectorspace V; x:V; y:V; z:V |] ==> |
|
423 |
(x = z - y) = (x + y = z)" |
|
424 |
(concl is "?L = ?R" ); |
|
425 |
proof -; |
|
426 |
assume vs: "is_vectorspace V" "x:V" "y:V" "z:V"; |
|
427 |
show "?L = ?R"; |
|
428 |
proof; |
|
429 |
assume ?L; |
|
430 |
hence "x + y = z - y + y"; by simp; |
|
431 |
also; have "... = z + - y + y"; by (simp! add: diff_eq1); |
|
432 |
also; have "... = z + (- y + y)"; |
|
433 |
by (rule vs_add_assoc) (simp!)+; |
|
434 |
also; from vs; have "... = z + <0>"; |
|
435 |
by (simp only: vs_add_minus_left); |
|
436 |
also; from vs; have "... = z"; by (simp only: vs_add_zero_right); |
|
7978 | 437 |
finally; show ?R; .; |
7917 | 438 |
next; |
439 |
assume ?R; |
|
440 |
hence "z - y = (x + y) - y"; by simp; |
|
441 |
also; from vs; have "... = x + y + - y"; |
|
442 |
by (simp add: diff_eq1); |
|
443 |
also; have "... = x + (y + - y)"; |
|
444 |
by (rule vs_add_assoc) (simp!)+; |
|
445 |
also; have "... = x"; by (simp!); |
|
446 |
finally; show ?L; by (rule sym); |
|
447 |
qed; |
|
448 |
qed; |
|
449 |
||
450 |
lemma vs_add_minus_eq_minus: |
|
7978 | 451 |
"[| is_vectorspace V; x:V; y:V; x + y = <0> |] ==> x = - y"; |
7917 | 452 |
proof -; |
453 |
assume "is_vectorspace V" "x:V" "y:V"; |
|
454 |
have "x = (- y + y) + x"; by (simp!); |
|
455 |
also; have "... = - y + (x + y)"; by (simp!); |
|
456 |
also; assume "x + y = <0>"; |
|
457 |
also; have "- y + <0> = - y"; by (simp!); |
|
458 |
finally; show "x = - y"; .; |
|
459 |
qed; |
|
460 |
||
461 |
lemma vs_add_minus_eq: |
|
462 |
"[| is_vectorspace V; x:V; y:V; x - y = <0> |] ==> x = y"; |
|
463 |
proof -; |
|
464 |
assume "is_vectorspace V" "x:V" "y:V" "x - y = <0>"; |
|
465 |
assume "x - y = <0>"; |
|
466 |
hence e: "x + - y = <0>"; by (simp! add: diff_eq1); |
|
467 |
with _ _ _; have "x = - (- y)"; |
|
468 |
by (rule vs_add_minus_eq_minus) (simp!)+; |
|
469 |
thus "x = y"; by (simp!); |
|
470 |
qed; |
|
471 |
||
472 |
lemma vs_add_diff_swap: |
|
7978 | 473 |
"[| is_vectorspace V; a:V; b:V; c:V; d:V; a + b = c + d |] |
7917 | 474 |
==> a - c = d - b"; |
475 |
proof -; |
|
476 |
assume vs: "is_vectorspace V" "a:V" "b:V" "c:V" "d:V" |
|
7978 | 477 |
and eq: "a + b = c + d"; |
7917 | 478 |
have "- c + (a + b) = - c + (c + d)"; |
479 |
by (simp! add: vs_add_left_cancel); |
|
480 |
also; have "... = d"; by (rule vs_minus_add_cancel); |
|
481 |
finally; have eq: "- c + (a + b) = d"; .; |
|
482 |
from vs; have "a - c = (- c + (a + b)) + - b"; |
|
483 |
by (simp add: vs_add_ac diff_eq1); |
|
484 |
also; from eq; have "... = d + - b"; |
|
485 |
by (simp! add: vs_add_right_cancel); |
|
486 |
also; have "... = d - b"; by (simp! add : diff_eq2); |
|
487 |
finally; show "a - c = d - b"; .; |
|
488 |
qed; |
|
489 |
||
490 |
lemma vs_add_cancel_21: |
|
7978 | 491 |
"[| is_vectorspace V; x:V; y:V; z:V; u:V |] |
7917 | 492 |
==> (x + (y + z) = y + u) = ((x + z) = u)" |
7978 | 493 |
(concl is "?L = ?R"); |
7917 | 494 |
proof -; |
495 |
assume "is_vectorspace V" "x:V" "y:V""z:V" "u:V"; |
|
496 |
show "?L = ?R"; |
|
497 |
proof; |
|
498 |
have "x + z = - y + y + (x + z)"; by (simp!); |
|
499 |
also; have "... = - y + (y + (x + z))"; |
|
500 |
by (rule vs_add_assoc) (simp!)+; |
|
501 |
also; have "y + (x + z) = x + (y + z)"; by (simp!); |
|
502 |
also; assume ?L; |
|
503 |
also; have "- y + (y + u) = u"; by (simp!); |
|
504 |
finally; show ?R; .; |
|
505 |
qed (simp! only: vs_add_left_commute [of V x]); |
|
506 |
qed; |
|
507 |
||
508 |
lemma vs_add_cancel_end: |
|
509 |
"[| is_vectorspace V; x:V; y:V; z:V |] |
|
510 |
==> (x + (y + z) = y) = (x = - z)" |
|
511 |
(concl is "?L = ?R" ); |
|
512 |
proof -; |
|
513 |
assume "is_vectorspace V" "x:V" "y:V" "z:V"; |
|
514 |
show "?L = ?R"; |
|
515 |
proof; |
|
516 |
assume l: ?L; |
|
517 |
have "x + z = <0>"; |
|
518 |
proof (rule vs_add_left_cancel [RS iffD1]); |
|
519 |
have "y + (x + z) = x + (y + z)"; by (simp!); |
|
520 |
also; note l; |
|
521 |
also; have "y = y + <0>"; by (simp!); |
|
522 |
finally; show "y + (x + z) = y + <0>"; .; |
|
523 |
qed (simp!)+; |
|
524 |
thus "x = - z"; by (simp! add: vs_add_minus_eq_minus); |
|
525 |
next; |
|
526 |
assume r: ?R; |
|
527 |
hence "x + (y + z) = - z + (y + z)"; by simp; |
|
528 |
also; have "... = y + (- z + z)"; |
|
529 |
by (simp! only: vs_add_left_commute); |
|
530 |
also; have "... = y"; by (simp!); |
|
531 |
finally; show ?L; .; |
|
532 |
qed; |
|
533 |
qed; |
|
534 |
||
535 |
end; |