When applied to a theorem A |- !p1...pn. t, the inference rule PSPEC_ALL
returns the theorem A |- t[p1'/p1]...[pn'/pn] where the pi' are distinct
variants of the corresponding pi, chosen to avoid clashes with any variables
free in the assumption list and with the names of constants. Normally pi' is
just pi, in which case PSPEC_ALL simply removes all universal quantifiers.
A |- !p1...pn. t
--------------------------- PSPEC_ALL
A |- t[p1'/x1]...[pn'/xn]