reserve n for Nat,
  i for Integer,
  p, x, x0, y for Real,
  q for Rational,
  f for PartFunc of REAL,REAL;

theorem Th15:
  y > 0 implies exp_R.(log(number_e,y)) = y
proof
  assume
A1: y > 0;
  thus exp_R.(log(number_e,y)) = exp_R(log(number_e,y)) by SIN_COS:def 23
    .= y by A1,Th14;
end;
