Step |
Hyp |
Ref |
Expression |
1 |
|
0lt1 |
|- 0 < 1 |
2 |
|
breq2 |
|- ( ( sgn ` ( A x. B ) ) = 1 -> ( 0 < ( sgn ` ( A x. B ) ) <-> 0 < 1 ) ) |
3 |
1 2
|
mpbiri |
|- ( ( sgn ` ( A x. B ) ) = 1 -> 0 < ( sgn ` ( A x. B ) ) ) |
4 |
3
|
adantl |
|- ( ( ( A e. RR /\ B e. RR ) /\ ( sgn ` ( A x. B ) ) = 1 ) -> 0 < ( sgn ` ( A x. B ) ) ) |
5 |
|
simplr |
|- ( ( ( ( A e. RR /\ B e. RR ) /\ 0 < ( sgn ` ( A x. B ) ) ) /\ ( sgn ` ( A x. B ) ) = -u 1 ) -> 0 < ( sgn ` ( A x. B ) ) ) |
6 |
|
simpr |
|- ( ( ( ( A e. RR /\ B e. RR ) /\ 0 < ( sgn ` ( A x. B ) ) ) /\ ( sgn ` ( A x. B ) ) = -u 1 ) -> ( sgn ` ( A x. B ) ) = -u 1 ) |
7 |
5 6
|
breqtrd |
|- ( ( ( ( A e. RR /\ B e. RR ) /\ 0 < ( sgn ` ( A x. B ) ) ) /\ ( sgn ` ( A x. B ) ) = -u 1 ) -> 0 < -u 1 ) |
8 |
|
1nn0 |
|- 1 e. NN0 |
9 |
|
nn0nlt0 |
|- ( 1 e. NN0 -> -. 1 < 0 ) |
10 |
8 9
|
ax-mp |
|- -. 1 < 0 |
11 |
|
1re |
|- 1 e. RR |
12 |
|
lt0neg1 |
|- ( 1 e. RR -> ( 1 < 0 <-> 0 < -u 1 ) ) |
13 |
11 12
|
ax-mp |
|- ( 1 < 0 <-> 0 < -u 1 ) |
14 |
10 13
|
mtbi |
|- -. 0 < -u 1 |
15 |
14
|
a1i |
|- ( ( ( ( A e. RR /\ B e. RR ) /\ 0 < ( sgn ` ( A x. B ) ) ) /\ ( sgn ` ( A x. B ) ) = -u 1 ) -> -. 0 < -u 1 ) |
16 |
7 15
|
pm2.21dd |
|- ( ( ( ( A e. RR /\ B e. RR ) /\ 0 < ( sgn ` ( A x. B ) ) ) /\ ( sgn ` ( A x. B ) ) = -u 1 ) -> ( sgn ` ( A x. B ) ) = 1 ) |
17 |
|
simpr |
|- ( ( ( ( A e. RR /\ B e. RR ) /\ 0 < ( sgn ` ( A x. B ) ) ) /\ ( sgn ` ( A x. B ) ) = 0 ) -> ( sgn ` ( A x. B ) ) = 0 ) |
18 |
|
simplr |
|- ( ( ( ( A e. RR /\ B e. RR ) /\ 0 < ( sgn ` ( A x. B ) ) ) /\ ( sgn ` ( A x. B ) ) = 0 ) -> 0 < ( sgn ` ( A x. B ) ) ) |
19 |
18
|
gt0ne0d |
|- ( ( ( ( A e. RR /\ B e. RR ) /\ 0 < ( sgn ` ( A x. B ) ) ) /\ ( sgn ` ( A x. B ) ) = 0 ) -> ( sgn ` ( A x. B ) ) =/= 0 ) |
20 |
17 19
|
pm2.21ddne |
|- ( ( ( ( A e. RR /\ B e. RR ) /\ 0 < ( sgn ` ( A x. B ) ) ) /\ ( sgn ` ( A x. B ) ) = 0 ) -> ( sgn ` ( A x. B ) ) = 1 ) |
21 |
|
simpr |
|- ( ( ( ( A e. RR /\ B e. RR ) /\ 0 < ( sgn ` ( A x. B ) ) ) /\ ( sgn ` ( A x. B ) ) = 1 ) -> ( sgn ` ( A x. B ) ) = 1 ) |
22 |
|
remulcl |
|- ( ( A e. RR /\ B e. RR ) -> ( A x. B ) e. RR ) |
23 |
22
|
rexrd |
|- ( ( A e. RR /\ B e. RR ) -> ( A x. B ) e. RR* ) |
24 |
23
|
adantr |
|- ( ( ( A e. RR /\ B e. RR ) /\ 0 < ( sgn ` ( A x. B ) ) ) -> ( A x. B ) e. RR* ) |
25 |
|
sgncl |
|- ( ( A x. B ) e. RR* -> ( sgn ` ( A x. B ) ) e. { -u 1 , 0 , 1 } ) |
26 |
|
eltpi |
|- ( ( sgn ` ( A x. B ) ) e. { -u 1 , 0 , 1 } -> ( ( sgn ` ( A x. B ) ) = -u 1 \/ ( sgn ` ( A x. B ) ) = 0 \/ ( sgn ` ( A x. B ) ) = 1 ) ) |
27 |
24 25 26
|
3syl |
|- ( ( ( A e. RR /\ B e. RR ) /\ 0 < ( sgn ` ( A x. B ) ) ) -> ( ( sgn ` ( A x. B ) ) = -u 1 \/ ( sgn ` ( A x. B ) ) = 0 \/ ( sgn ` ( A x. B ) ) = 1 ) ) |
28 |
16 20 21 27
|
mpjao3dan |
|- ( ( ( A e. RR /\ B e. RR ) /\ 0 < ( sgn ` ( A x. B ) ) ) -> ( sgn ` ( A x. B ) ) = 1 ) |
29 |
4 28
|
impbida |
|- ( ( A e. RR /\ B e. RR ) -> ( ( sgn ` ( A x. B ) ) = 1 <-> 0 < ( sgn ` ( A x. B ) ) ) ) |
30 |
|
sgnpbi |
|- ( ( A x. B ) e. RR* -> ( ( sgn ` ( A x. B ) ) = 1 <-> 0 < ( A x. B ) ) ) |
31 |
23 30
|
syl |
|- ( ( A e. RR /\ B e. RR ) -> ( ( sgn ` ( A x. B ) ) = 1 <-> 0 < ( A x. B ) ) ) |
32 |
|
sgnmul |
|- ( ( A e. RR /\ B e. RR ) -> ( sgn ` ( A x. B ) ) = ( ( sgn ` A ) x. ( sgn ` B ) ) ) |
33 |
32
|
breq2d |
|- ( ( A e. RR /\ B e. RR ) -> ( 0 < ( sgn ` ( A x. B ) ) <-> 0 < ( ( sgn ` A ) x. ( sgn ` B ) ) ) ) |
34 |
29 31 33
|
3bitr3d |
|- ( ( A e. RR /\ B e. RR ) -> ( 0 < ( A x. B ) <-> 0 < ( ( sgn ` A ) x. ( sgn ` B ) ) ) ) |