Metamath Proof Explorer


Theorem ringlidm

Description: The unity element of a ring is a left multiplicative identity. (Contributed by NM, 15-Sep-2011)

Ref Expression
Hypotheses ringidm.b
|- B = ( Base ` R )
ringidm.t
|- .x. = ( .r ` R )
ringidm.u
|- .1. = ( 1r ` R )
Assertion ringlidm
|- ( ( R e. Ring /\ X e. B ) -> ( .1. .x. X ) = X )

Proof

Step Hyp Ref Expression
1 ringidm.b
 |-  B = ( Base ` R )
2 ringidm.t
 |-  .x. = ( .r ` R )
3 ringidm.u
 |-  .1. = ( 1r ` R )
4 1 2 3 ringidmlem
 |-  ( ( R e. Ring /\ X e. B ) -> ( ( .1. .x. X ) = X /\ ( X .x. .1. ) = X ) )
5 4 simpld
 |-  ( ( R e. Ring /\ X e. B ) -> ( .1. .x. X ) = X )