theorem Th4:
  not x in variables_in H implies (M,v |= H iff M,v |= All(x,H))
proof
  Free H c= variables_in H by ZF_LANG1:151;
  then
A1: x in Free H implies x in variables_in H;
  v/(x,v.x) = v by FUNCT_7:35;
  hence thesis by A1,ZFMODEL1:10,ZF_LANG1:71;
end;
