6.1. (5 points) Is the following statement a tautology, a contradiction, or neither? You need to provide a rigorous explanation or proof.
∄a. ∀b (b∈a↔b∉b)\nexists a.\, \forall b\, (b \in a \leftrightarrow b \notin b)∄a.∀b(b∈a↔b∈/b)
