NAME
    comb - combinatorial number

SYNOPSIS
    comb(x, y)

TYPES
    x		integer
    y		integer

    return	integer

DESCRIPTION
    Return the combinatorial number C(x,y) which is defined as:

	       x!
	    ---------
	    y!*(x-y)!

    This function computes the number of combinations in which y things
    may be chosen from x items ignoring the order in which they are chosen.

EXAMPLE
    > print comb(7,3), comb(7,4), comb(7,5), comb(3,0), comb(0,0)
    35 35 21 1 1

    > print comb(2^31+1,2^31-1)
    2305843010287435776

LIMITS
    x >= y >= 0
    y < 2^24
    x-y < 2^24

LIBRARY
    void zcomb(ZVALUE x, ZVALUE y, ZVALUE *res)

SEE ALSO
    fact, perm