reserve a,b,c,x,y,z for Real;

theorem Th44:
  a <= 0 & x < a implies x^2 > a^2
proof
  assume that
A1: a<=0 and
A2: x<a;
  -x>-a by A2,XREAL_1:24;
  then (-x)^2>(-a)^2 by A1,Th16;
  hence thesis;
end;
