 We are free to step back and think of these as equations which we hope to solve.   For example, we could take the set N as known, regard N∞ as a variable, and then consider an equation like X = N×X.     However, the  none of these is the kind of equation that we could hope to solve in a perfectly general way using AFA: the right-hand sides are  not given in terms of sets of objects on the left. Solving more complicated systems takes special additional  work. Here is what is known on this. 