If two integers *a* and *b* have the same remainder when divided by
positive integer *n*, then we say that *a* and *b* are congruent modulo
*n*. This is written (mod *n*). For example,
(mod 3). It is not hard to see that (mod *n*) is
equivalent to *a*-*b* being a multiple of *n*.

Wed Apr 21 08:17:28 EDT 1999