reserve x for set;
reserve a, b, c, d, e for Real;
reserve m, n, m1, m2 for Nat;
reserve k, l for Integer;
reserve p for Rational;

theorem
  a>0 & a<>1 implies log(a,1) = 0
proof
  assume
A1: a>0 & a<>1;
 a to_power 0 = 1 by Th24;
  hence thesis by A1,Def3;
end;
