reserve r, s, t for Real;
reserve seq for Real_Sequence,
  X, Y for Subset of REAL;
reserve r3, r1, q3, p3 for Real;

theorem Th66:
  for X being non empty set, f being Function of X, REAL holds
  f is with_min iff -f is with_max
proof
  let X be non empty set, f be Function of X, REAL;
  - -f = f;
  hence thesis by Lm9,Lm10;
end;
