reserve x,y,t for Real;

theorem Th23:
  1<=x implies 0<x+sqrt(x^2-1)
proof
  assume
A1: 1<=x;
  then x^2-1>=0 by Lm3;
  then 0<=sqrt(x^2-1) by SQUARE_1:def 2;
  hence thesis by A1;
end;
