Metamath Proof Explorer


Theorem mapdordlem1

Description: Lemma for mapdord . (Contributed by NM, 27-Jan-2015)

Ref Expression
Hypothesis mapdordlem1.t
|- T = { g e. F | ( O ` ( O ` ( L ` g ) ) ) e. Y }
Assertion mapdordlem1
|- ( J e. T <-> ( J e. F /\ ( O ` ( O ` ( L ` J ) ) ) e. Y ) )

Proof

Step Hyp Ref Expression
1 mapdordlem1.t
 |-  T = { g e. F | ( O ` ( O ` ( L ` g ) ) ) e. Y }
2 2fveq3
 |-  ( g = J -> ( O ` ( L ` g ) ) = ( O ` ( L ` J ) ) )
3 2 fveq2d
 |-  ( g = J -> ( O ` ( O ` ( L ` g ) ) ) = ( O ` ( O ` ( L ` J ) ) ) )
4 3 eleq1d
 |-  ( g = J -> ( ( O ` ( O ` ( L ` g ) ) ) e. Y <-> ( O ` ( O ` ( L ` J ) ) ) e. Y ) )
5 4 1 elrab2
 |-  ( J e. T <-> ( J e. F /\ ( O ` ( O ` ( L ` J ) ) ) e. Y ) )