Metamath Proof Explorer

Theorem imbi2i

Description: Introduce an antecedent to both sides of a logical equivalence. This and the next three rules are useful for building up wff's around a definition, in order to make use of the definition. (Contributed by NM, 3-Jan-1993) (Proof shortened by Wolf Lammen, 6-Feb-2013)

Ref Expression
Hypothesis imbi2i.1 φ ψ
Assertion imbi2i χ φ χ ψ


Step Hyp Ref Expression
1 imbi2i.1 φ ψ
2 1 a1i χ φ ψ
3 2 pm5.74i χ φ χ ψ