When applied to a list of paired variable structures [p1;...;pn]
and a theorem A |- t, the inference rule PGENL returns
the theorem A |- !p1...pn. t, provided none of the constituent variables
from any of the pairs pi occur free in the assumptions.
         A |- t
   ------------------  PGENL "[p1;...;pn]"       [where no pi is free in A]
    A |- !p1...pn. t