Let

*R* be a

commutative integral domain and let

*a,b*
be elements of

*R*. We say that

*a* divides *b* if
there exists

*c* in

*R* such that

*ac=b*.
In this case we write

*a|b*.

This is most familiar when *R*=**Z**, the integers.
For example, *2|4* but *2* doesn't divide *3*.