Theorem xppi12 | index | src |

theorem xppi12 (A B C: set) (a: nat): $ a e. Xp (Xp A B) C -> pi12 a e. B $;
StepHypRefExpression
1 xpfst
a e. Xp (Xp A B) C -> fst a e. Xp A B
2 xpsnd
fst a e. Xp A B -> snd (fst a) e. B
3 2 conv pi12
fst a e. Xp A B -> pi12 a e. B
4 1, 3 rsyl
a e. Xp (Xp A B) C -> pi12 a e. B

Axiom use

axs_prop_calc (ax_1, ax_2, ax_3, ax_mp, itru), axs_pred_calc (ax_gen, ax_4, ax_5, ax_6, ax_7, ax_10, ax_11, ax_12), axs_set (elab, ax_8), axs_the (theid, the0), axs_peano (peano1, peano2, peano5, addeq, muleq, add0, addS, mul0, mulS)