reserve c, c1, c2, d, d1, d2, e, y for Real,
  k, n, m, N, n1, N0, N1, N2, N3, M for Element of NAT,
  x for set;

theorem
  for a,b,c being Real st a>1 & b>=a & c>=1 holds
  log(a,c) >= log(b,c) by Lm19;
