do biconditonal statements?

Question

contain the phrase "if and only if'?

Answer 1

Most often, yes--and they always could be written with "if and only if". If is certainly possible to write them in other ways, though. Pretty much any definition like "a square is a qaudrilateral with four equal sides and four equal angles" is a biconditional statement. That's because if you wanted to, you could say "a quadrilateral is a square if and only if it has four equal sides and four equal angles".

Answer 2

indeed they do