theorem sreceq1d (_G: wff) (_S1 _S2: set) (n: nat): $ _G -> _S1 == _S2 $ > $ _G -> srec _S1 n = srec _S2 n $;
_G -> _S1 == _S2
_G -> n = n
_G -> srec _S1 n = srec _S2 n