Metamath Proof Explorer


Theorem normlem8

Description: Lemma used to derive properties of norm. (Contributed by NM, 30-Jun-2005) (New usage is discouraged.)

Ref Expression
Hypotheses normlem8.1 A
normlem8.2 B
normlem8.3 C
normlem8.4 D
Assertion normlem8 A + B ih C + D = A ih C + B ih D + A ih D + B ih C

Proof

Step Hyp Ref Expression
1 normlem8.1 A
2 normlem8.2 B
3 normlem8.3 C
4 normlem8.4 D
5 his7 A C D A ih C + D = A ih C + A ih D
6 1 3 4 5 mp3an A ih C + D = A ih C + A ih D
7 his7 B C D B ih C + D = B ih C + B ih D
8 2 3 4 7 mp3an B ih C + D = B ih C + B ih D
9 6 8 oveq12i A ih C + D + B ih C + D = A ih C + A ih D + B ih C + B ih D
10 3 4 hvaddcli C + D
11 ax-his2 A B C + D A + B ih C + D = A ih C + D + B ih C + D
12 1 2 10 11 mp3an A + B ih C + D = A ih C + D + B ih C + D
13 1 3 hicli A ih C
14 2 4 hicli B ih D
15 1 4 hicli A ih D
16 2 3 hicli B ih C
17 13 14 15 16 add42i A ih C + B ih D + A ih D + B ih C = A ih C + A ih D + B ih C + B ih D
18 9 12 17 3eqtr4i A + B ih C + D = A ih C + B ih D + A ih D + B ih C