reserve x,y,t for Real;

theorem Th30:
  0<>x implies (exp_R x)^2-1<>0
proof
  assume
A1: 0<>x;
  assume (exp_R x)^2-1=0;
  then exp_R x=1 or exp_R x= -1 by XCMPLX_1:182;
  hence contradiction by A1,Th29,SIN_COS:55;
end;
