Theorem bitr2 ≪ | index | src | ≫ 

theorem bitr2 (a b c: wff): $ (a <-> b) -> (b <-> c) -> (c <-> a) $;
StepHypRefExpression
1 anl 
(a <-> b) /\ (b <-> c) -> (a <-> b)
2 anr 
(a <-> b) /\ (b <-> c) -> (b <-> c)
3 1, 2 bitr2d 
(a <-> b) /\ (b <-> c) -> (c <-> a)
4 3 exp 
(a <-> b) -> (b <-> c) -> (c <-> a)

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp)