reserve x,y,z,w for ExtReal,
  r for Real;
reserve f,g for ExtReal;
reserve t for ExtReal;

theorem Th102:
  x < y & z < 0 & z <> -infty implies y*z < x*z
proof
  assume x < y & z < 0 & z <> -infty;
  then
A1: x*(-z) < y*(-z) by Th5,Th10,Th72;
  -x*z = x*(-z) & -y*z = y*(-z) by Th92;
  hence thesis by A1,Th38;
end;
