reserve x, y for set;

theorem Th2:
  for c be Real st c < 0 holds exp_R c < 1
  proof
    let c be Real;
    assume c < 0;
    then exp_R c <= 1 & exp_R c <> 1 by SIN_COS:53,SIN_COS7:29;
    hence thesis by XXREAL_0:1;
  end;
