theorem Th14:
  All(x1,y1,p1) = All(x2,y2,p2) implies x1 = x2 & y1 = y2 & p1 = p2
proof
  assume
A1: All(x1,y1,p1) = All(x2,y2,p2);
  then All(y1,p1) = All(y2,p2) by ZF_LANG:3;
  hence thesis by A1,ZF_LANG:3;
end;
