reserve x,y,t for Real;

theorem Th24:
  1<=x & 1<=y implies 0<=x*sqrt(y^2-1)+y*sqrt(x^2-1)
proof
  assume that
A1: 1<=x and
A2: 1<=y;
  0<=y^2-1 by A2,Lm3;
  then
A3: 0<=sqrt(y^2-1) by SQUARE_1:def 2;
  0<=x^2-1 by A1,Lm3;
  then 0<=sqrt(x^2-1) by SQUARE_1:def 2;
  hence thesis by A1,A2,A3;
end;
