|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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|Hoyningen-Huene II 131
Biconditional/HH: ↔ is a sign of metalogic - logical equivalence is a statement linking of the object language.
Equivalence/HH: weakening the identity of statements - equi statements are not in all respects the same, but only in a logical sense - both have always same truth values - equivalent formulas have the same inference sets - and they can be inferred from the same conditions.
Me I Albert Menne Folgerichtig Denken Darmstadt 1988
HH II Hoyningen-Huene Formale Logik, Stuttgart 1998
Re III Stephen Read Philosophie der Logik Hamburg 1997
Sal IV Wesley C. Salmon Logik Stuttgart 1983
Sai V R.M.Sainsbury Paradoxien Stuttgart 2001