bi.bldbi<>

Theorem.

Arguments:

phi (pr), psi (pr), chi (pr), theta (pr),

Hypotheses:

(chileftrightarrowtheta)
(phileftrightarrowpsi)

Assertions:

((phileftrightarrowchi)leftrightarrow(psileftrightarrowtheta))

Proof:

Hyp Ref Line Expr
Hypo1(chileftrightarrowtheta)
2(phileftrightarrowpsi)
2bi.bldbi<3((phileftrightarrowchi)leftrightarrow(psileftrightarrowchi))
1bi.bldbi>4((psileftrightarrowchi)leftrightarrow(psileftrightarrowtheta))
3, 4bitr5((phileftrightarrowchi)leftrightarrow(psileftrightarrowtheta))