`inv'
-----

inv(I,M)
     :: the inverse (reciprocal) of I modulo M.

RETURN
     integer

I M
     integer

   * This function computes an integer such that IA == 1 mod (M).

   * The integer I and  M must be mutually prime.  However, `inv()'
     does not check it.

     [71] igcd(1234,4321);
     1
     [72] inv(1234,4321);
     3239
     [73] irem(3239*1234,4321);
     1

References
     *Note `igcd igcdcntl': igcd igcdcntl.

