Theorem orld ≪ | index | src | ≫ 

theorem orld (a b c: wff): $ a -> b $ > $ a -> b \/ c $;
StepHypRefExpression
1 orl 
b -> b \/ c
2 hyp h 
a -> b
3 1, 2 syl 
a -> b \/ c

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp)