The Biconditional command can only be used when you
have a goal of the form P
Q.
If you select a goal of this form and give the Biconditional command, then
Proof Designer will create two subproofs, one for the proof of P
Q and one for the proof of Q
P. The two subproofs are labeled with
the symbols
and
, representing the two directions of the biconditional symbol
.