Explain why all propositional forms with two variables are logically equivalent with 1 to 16 possibilities.

two propositions are called logically equivalent if, and only if, when same proposition  variables (or sentential variables) are used to represent identical compound propositions, their forms are logically equivalent.

For instance, the negation of the negation (or double negation) of a proposition is logically equivalent to the proposition.

4 x4 possibilities = 16