
theorem NP0:
  for n be odd Nat holds n choose ((n + 1)/2) = n choose ((n - 1)/2)
  proof
    let n be odd Nat;
    reconsider k = (n - 1)/2 as Nat;
    (k + (k + 1)) choose k = (k + (k + 1)) choose (k + 1) by N20;
    hence thesis;
  end;
