When eliminating redundant states in the state table of a sequential circuit, we need to find equivalent states in the same circuit. In Fundamentals of Logic Design, two states are equivalent if and only if the states have the same next states and the same present outputs. The problem is, what if the next states of two states are each other?

As an example, consider the following state table (X is the circuit input):

The only difference between states A and B is that their next states are each other. Because you need to show two states have the same next states to prove they are equivalent, it follows that you need to show A=B in order to prove A=B, i.e., A=B iff A=B. Given this requirement, I am not sure how to go about proving A=B. The textbook dismisses this as self-implied. I can kind of see that they are equivalent, but I don't know how to get past the conundrum that you need to prove a statement "C" first before you can show "C" is true.