;;; MODULAR-INVERSE (x p)                                            [FUNCTION]
;;;    Find the inverse of X modulo prime P, using Euclid algorithm.
;;;
;;; MODULAR-DIVISION (x y p)                                         [FUNCTION]
;;;    Divide X by Y modulo prime P.
;;;
;;; *INVERSE-BY-LOOKUP-LIMIT* (100000)                               [VARIABLE]
;;;    If prime modulus is < this number then the division algorithm
;;;    will use a lookup table of inverses created at the time when
;;;    field-modulo-prime is called. 
;;;
;;; MAKE-INVERSE-TABLE (modulus &aux (table (list 0)))               [FUNCTION]
;;;    Make a vector of length MODULUS containing all inverses modulo
;;;    MODULUS, which should be a prime number. The inverse of 0 is 0.
;;;
;;; MAKE-MODULAR-DIVISION (modulus)                                  [FUNCTION]
;;;    Return a function of two arguments which will perform division
;;;    modulo MODULUS. Currently, if MODULUS is < *INVERSE-BY-LOOKUP-LIMIT*
;;;    then the returned function does table lookup, otherwise it uses
;;;    the Euclid algorithm to find the inverse.
;;;