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Metamath Proof Explorer

Theorem mul32

Description: Commutative/associative law. (Contributed by NM, 8-Oct-1999)

Ref Expression
Assertion mul32 
|- ( ( A e. CC /\ B e. CC /\ C e. CC ) -> ( ( A x. B ) x. C ) = ( ( A x. C ) x. B ) )

Proof

Step Hyp Ref Expression
1 mulcom 
 |-  ( ( B e. CC /\ C e. CC ) -> ( B x. C ) = ( C x. B ) )
2 1 oveq2d 
 |-  ( ( B e. CC /\ C e. CC ) -> ( A x. ( B x. C ) ) = ( A x. ( C x. B ) ) )
3 2 3adant1 
 |-  ( ( A e. CC /\ B e. CC /\ C e. CC ) -> ( A x. ( B x. C ) ) = ( A x. ( C x. B ) ) )
4 mulass 
 |-  ( ( A e. CC /\ B e. CC /\ C e. CC ) -> ( ( A x. B ) x. C ) = ( A x. ( B x. C ) ) )
5 mulass 
 |-  ( ( A e. CC /\ C e. CC /\ B e. CC ) -> ( ( A x. C ) x. B ) = ( A x. ( C x. B ) ) )
6 5 3com23 
 |-  ( ( A e. CC /\ B e. CC /\ C e. CC ) -> ( ( A x. C ) x. B ) = ( A x. ( C x. B ) ) )
7 3 4 6 3eqtr4d 
 |-  ( ( A e. CC /\ B e. CC /\ C e. CC ) -> ( ( A x. B ) x. C ) = ( ( A x. C ) x. B ) )