|Equivalence: Relation between sentences. It exists if both sides have the same truth value, so that they are both true or both false.|
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Bisubjunktion / (biconditional) / Wessel: an operator that makes one formula out of two - equivalence: no Operator, but sentence which asserts the equivalence of two formulas - the formulas are not even in the equivalence but quoted: "Formula A" , equi "formula B"
Logik Berlin 1999