Metamath Proof Explorer


Theorem imbi2

Description: Theorem *4.85 of WhiteheadRussell p. 122. (Contributed by NM, 3-Jan-2005) (Proof shortened by Wolf Lammen, 19-May-2013)

Ref Expression
Assertion imbi2 φ ψ χ φ χ ψ

Proof

Step Hyp Ref Expression
1 id φ ψ φ ψ
2 1 imbi2d φ ψ χ φ χ ψ