reserve x, y, z, r, s, t for Real;

theorem :: SQUARE_1:98
  0 <= x*y implies sqrt (x*y) = sqrt |.x.|*sqrt |.y.|
proof
  assume 0 <= x*y;
  then |.x*y.| = x*y by Def1;
  then
A1: |.x.|*|.y.| = x*y by COMPLEX1:65;
  0 <= |.x.| & 0 <= |.y.| by COMPLEX1:46;
  hence thesis by A1,SQUARE_1:29;
end;
