Metamath Proof Explorer


Theorem mulgt0con1d

Description: Counterpart to mulgt0con2d , though not a lemma of anything. This is the first use of ax-pre-mulgt0 . (Contributed by SN, 26-Jun-2024)

Ref Expression
Hypotheses mulgt0con1d.a
|- ( ph -> A e. RR )
mulgt0con1d.b
|- ( ph -> B e. RR )
mulgt0con1d.1
|- ( ph -> 0 < B )
mulgt0con1d.2
|- ( ph -> ( A x. B ) < 0 )
Assertion mulgt0con1d
|- ( ph -> A < 0 )

Proof

Step Hyp Ref Expression
1 mulgt0con1d.a
 |-  ( ph -> A e. RR )
2 mulgt0con1d.b
 |-  ( ph -> B e. RR )
3 mulgt0con1d.1
 |-  ( ph -> 0 < B )
4 mulgt0con1d.2
 |-  ( ph -> ( A x. B ) < 0 )
5 1 2 remulcld
 |-  ( ph -> ( A x. B ) e. RR )
6 1 adantr
 |-  ( ( ph /\ 0 < A ) -> A e. RR )
7 2 adantr
 |-  ( ( ph /\ 0 < A ) -> B e. RR )
8 simpr
 |-  ( ( ph /\ 0 < A ) -> 0 < A )
9 3 adantr
 |-  ( ( ph /\ 0 < A ) -> 0 < B )
10 6 7 8 9 mulgt0d
 |-  ( ( ph /\ 0 < A ) -> 0 < ( A x. B ) )
11 10 ex
 |-  ( ph -> ( 0 < A -> 0 < ( A x. B ) ) )
12 remul02
 |-  ( B e. RR -> ( 0 x. B ) = 0 )
13 2 12 syl
 |-  ( ph -> ( 0 x. B ) = 0 )
14 oveq1
 |-  ( A = 0 -> ( A x. B ) = ( 0 x. B ) )
15 14 eqeq1d
 |-  ( A = 0 -> ( ( A x. B ) = 0 <-> ( 0 x. B ) = 0 ) )
16 13 15 syl5ibrcom
 |-  ( ph -> ( A = 0 -> ( A x. B ) = 0 ) )
17 1 5 11 16 mulgt0con1dlem
 |-  ( ph -> ( ( A x. B ) < 0 -> A < 0 ) )
18 4 17 mpd
 |-  ( ph -> A < 0 )