const func bigInteger: (in bigInteger: n) ! (in var bigInteger: k) is func
  result
    var bigInteger: binom is 0_;
  local
    var bigInteger: numerator is 0_;
    var bigInteger: denominator is 0_;
  begin
    if n >= 0_ and k > n >> 1 then
      k := n - k;
    end if;
    if k < 0_ then
      binom := 0_;
    elsif k = 0_ then
      binom := 1_;
    else
      binom := n;
      numerator := pred(n);
      denominator := 2_;
      while denominator <= k do
        binom *:= numerator;
        binom := binom div denominator;
        decr(numerator);
        incr(denominator);
      end while;
    end if;
  end func;