Step |
Hyp |
Ref |
Expression |
1 |
|
lemul1 |
|- ( ( A e. RR /\ B e. RR /\ ( C e. RR /\ 0 < C ) ) -> ( A <_ B <-> ( A x. C ) <_ ( B x. C ) ) ) |
2 |
|
recn |
|- ( A e. RR -> A e. CC ) |
3 |
|
recn |
|- ( C e. RR -> C e. CC ) |
4 |
|
mulcom |
|- ( ( A e. CC /\ C e. CC ) -> ( A x. C ) = ( C x. A ) ) |
5 |
2 3 4
|
syl2an |
|- ( ( A e. RR /\ C e. RR ) -> ( A x. C ) = ( C x. A ) ) |
6 |
5
|
3adant2 |
|- ( ( A e. RR /\ B e. RR /\ C e. RR ) -> ( A x. C ) = ( C x. A ) ) |
7 |
|
recn |
|- ( B e. RR -> B e. CC ) |
8 |
|
mulcom |
|- ( ( B e. CC /\ C e. CC ) -> ( B x. C ) = ( C x. B ) ) |
9 |
7 3 8
|
syl2an |
|- ( ( B e. RR /\ C e. RR ) -> ( B x. C ) = ( C x. B ) ) |
10 |
9
|
3adant1 |
|- ( ( A e. RR /\ B e. RR /\ C e. RR ) -> ( B x. C ) = ( C x. B ) ) |
11 |
6 10
|
breq12d |
|- ( ( A e. RR /\ B e. RR /\ C e. RR ) -> ( ( A x. C ) <_ ( B x. C ) <-> ( C x. A ) <_ ( C x. B ) ) ) |
12 |
11
|
3adant3r |
|- ( ( A e. RR /\ B e. RR /\ ( C e. RR /\ 0 < C ) ) -> ( ( A x. C ) <_ ( B x. C ) <-> ( C x. A ) <_ ( C x. B ) ) ) |
13 |
1 12
|
bitrd |
|- ( ( A e. RR /\ B e. RR /\ ( C e. RR /\ 0 < C ) ) -> ( A <_ B <-> ( C x. A ) <_ ( C x. B ) ) ) |