Theorem nfab1 | index | src |

theorem nfab1 {x: nat} (p: wff x): $ FS/ x {x | p} $;
StepHypRefExpression
1 elab
y e. {x | p} <-> [y / x] p
2 nfsb1
F/ x [y / x] p
3 1, 2 nfx
F/ x y e. {x | p}
4 3 nfsri
FS/ x {x | p}

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)