Theorem fsteqd | index | src |

theorem fsteqd (_G: wff) (_a1 _a2: nat):
  $ _G -> _a1 = _a2 $ >
  $ _G -> fst _a1 = fst _a2 $;
StepHypRefExpression
1 hyp _ah
_G -> _a1 = _a2
2 eqidd
_G -> x, y = x, y
3 1, 2 eqeqd
_G -> (_a1 = x, y <-> _a2 = x, y)
4 3 exeqd
_G -> (E. y _a1 = x, y <-> E. y _a2 = x, y)
5 4 abeqd
_G -> {x | E. y _a1 = x, y} == {x | E. y _a2 = x, y}
6 5 theeqd
_G -> the {x | E. y _a1 = x, y} = the {x | E. y _a2 = x, y}
7 6 conv fst
_G -> fst _a1 = fst _a2

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)