|Biconditional: notation ↔; a statement that is true if the two sides have the same truth value ("true" or "false"). The biconditional (also bisubjunction) is part of the object language. Contrary to that is equivalence (⇔) which belongs to meta language. A biconditional that is always true is an equivalence.|
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Biconditional, weak: A B is weak valid if no statement can be true without the other even when both are evaluated differently (assertibility, renunciation of bivalence) - strong: if A and B are always necessarily given the same evaluation.
Wahrheit und Objektivität Frankfurt 2001