theorem alleq2d (_G: wff) (A: set) (_l1 _l2: nat): $ _G -> _l1 = _l2 $ > $ _G -> (all A _l1 <-> all A _l2) $;
_G -> A == A
_G -> _l1 = _l2
_G -> (all A _l1 <-> all A _l2)