From ea271b82db4a090ea4d3939baba814d2d077513d Mon Sep 17 00:00:00 2001
From: Cyril Cohen
Date: Thu, 16 Nov 2017 14:28:06 +0100
Subject: Add addrKA and subrKA (addrK and addrNK modulo Associativity)

---
 mathcomp/algebra/ssralg.v | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/mathcomp/algebra/ssralg.v b/mathcomp/algebra/ssralg.v
index 9d93608..8ae63b8 100644
--- a/mathcomp/algebra/ssralg.v
+++ b/mathcomp/algebra/ssralg.v
@@ -732,6 +732,12 @@ Proof. by apply: (canRL (addrK x)); rewrite addrC subKr. Qed.
 Lemma opprD : {morph -%R: x y / x + y : V}.
 Proof. by move=> x y; rewrite -[y in LHS]opprK opprB addrC. Qed.
 
+Lemma addrKA z x y : (x + z) - (z + y) = x - y.
+Proof. by rewrite opprD addrA addrK. Qed.
+
+Lemma subrKA z x y : (x - z) + (z - y) = x - y.
+Proof. by rewrite addrA addrNK. Qed.
+
 Lemma subr0_eq x y : x - y = 0 -> x = y.
 Proof. by rewrite -(subrr y) => /addIr. Qed.
 
-- 
cgit v1.2.3


From 848bcdb47a7e8d8da0e1cd5530a3feadcac93ede Mon Sep 17 00:00:00 2001
From: Cyril Cohen
Date: Mon, 27 Nov 2017 14:36:14 +0100
Subject: following @ggonthier remark.

---
 mathcomp/algebra/ssralg.v | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mathcomp/algebra/ssralg.v b/mathcomp/algebra/ssralg.v
index 8ae63b8..859bb1d 100644
--- a/mathcomp/algebra/ssralg.v
+++ b/mathcomp/algebra/ssralg.v
@@ -735,7 +735,7 @@ Proof. by move=> x y; rewrite -[y in LHS]opprK opprB addrC. Qed.
 Lemma addrKA z x y : (x + z) - (z + y) = x - y.
 Proof. by rewrite opprD addrA addrK. Qed.
 
-Lemma subrKA z x y : (x - z) + (z - y) = x - y.
+Lemma subrKA z x y : (x - z) + (z + y) = x + y.
 Proof. by rewrite addrA addrNK. Qed.
 
 Lemma subr0_eq x y : x - y = 0 -> x = y.
-- 
cgit v1.2.3