All infix operations in the weakest priority group (those containing
at least one of the characters '=', '<', '>', or '~') are considered
non-associative and the chains (t1 OP t2 OP t3) are translated into
conjunctions (t1 OP t2 /\ t2 OP t3).

This does not concern implication '->' and equivalence '<->'
which are right-associative. like the rest of propositional
connectives.