theorem Th160:
  All(y,G) = All(x,H)/(x,y) iff G = H/(x,y)
proof
  thus All(y,G) = All(x,H)/(x,y) implies G = H/(x,y)
  proof
    assume All(y,G) = All(x,H)/(x,y);
    then All(y,G) = All(y,H/(x,y)) by Lm2;
    hence thesis by ZF_LANG:3;
  end;
  thus thesis by Lm2;
end;
