theorem Th75:
  not x in still_not-bound_in p implies (p => All(x,q)) <=> All(x,
  p => q) is valid
proof
  assume not x in still_not-bound_in p;
  then
  (p => All(x,q)) => All(x,p => q) is valid & All(x,p => q) => (p => All(x
  ,q)) is valid by Th74;
  hence thesis by Lm14;
end;
