
theorem Th10:
  for a, b, c being Real st a > 1 & b > 0 & c >= b holds
  log (a, c) >= log (a, b)
proof
  let a, b, c be Real;
  assume that
A1: a > 1 & b > 0 and
A2: c >= b;
  c > b or c = b by A2,XXREAL_0:1;
  hence thesis by A1,POWER:57;
end;
