'A is true because B is true; B is true because A is true.' This type of argument is termed

"A is true because B, and B is true because A" is a circular argument.

Each claim is supported only by the other claim.

The conclusion is thus used to prove its own premise.

No independent ground outside the circle is ever offered.

This reasoning in a closed loop is the fallacy of circularity, or begging the question.