Metamath Proof Explorer


Theorem bitr4di

Description: A syllogism inference from two biconditionals. (Contributed by NM, 12-Mar-1993)

Ref Expression
Hypotheses bitr4di.1 φψχ
bitr4di.2 θχ
Assertion bitr4di φψθ

Proof

Step Hyp Ref Expression
1 bitr4di.1 φψχ
2 bitr4di.2 θχ
3 2 bicomi χθ
4 1 3 bitrdi φψθ