Suppose there were three events that could be done in any order. Let these events be A, B and C. There are a total of 6 possible ways the events can be performed.

However, this time, there is a restriction. B can only be performed after A. In other words, A must be performed before B can, and ACB is also accepted.

Your task is to find a general formula for X number of events, and Y number of restrictions.

None of the events is mentioned in more than one restriction.