Solves first order, linear recurrence equations.

A first order linear recurrence equation in y(k) is  where A(k), B(k), and C(k) are independent of y(k).

If A(k) is undefined for some k, then a set of equations may be returned, giving values of y(k) for specific k as well as the general formula.

See the help page for LREtools[REcreate] for the definition of the format of a problem.