fencepost problem

Etymology
By analogy with fence-building. If one wants to say "lay a fencepost, then a length of fence, then repeat", then a special case must be made for the final fencepost. If one wants to say "lay a length of fence, then a fencepost, then repeat", then a special case must be made for the initial fencepost.

Noun

 * 1)  A problem dealing with how to treat the initial or boundary values of a discrete problem.