; This example demonstrates how to use Mercury's built-in
; FACT function (FACT(x) = x factorial).  The problem is:
; In a bridge game, the declarer controls 7 trump cards.
; We must determine the probability that the remaining
; 6 trump cards are evenly distributed (3 and 3) among
; the opposing two players.  We calculate both the
; approximate and the exact probability in this example.

; the binomial coefficient formula
; ways of choosing k of n items
C(n,k) := BINOM(n,k)     ; = FACT(n) / (FACT(k) FACT(n-k))

; approximate probability of 3-3 split
  ProbApprox = C(6,3) / 2^6

; exact probability of 3-3 split
  ProbExact = C(6,3) * C(20,10) / C(26,13)