FACTORIAL (_) For a non-negative integer argument y, the definition is */>:i.y. In general, !y is gamma >:y.
OUT OF (COMBINATIONS) (0 0) For non-negative arguments x!y is the number of ways that x things can be chosen out of y. More generally, out of (x!y) is defined as (!y)%(!x)*(!yΓÇôx) with the understanding that infinities (occasioned by ! on a negative integer) cancel if they occur in both numerator and denominator. Thus: