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Def Inference/Mates: exists when the associated subjunction (Ante/Suc) is valid.
Def Inference/Mates: is a statement j of a set G of statements, iff there is no interpretation where all statements of G are true and j is false.
Def Consistent: is a set G of statements if there is an interpretation where no statements of G are true. (Here, consistency = satisfiable) - Def satisfiability: a set G of statements is satisfiable if there is an interpretation in which all statements of G are true (= consistent).
Problem: this does not enable us to decide whether a statement is valid, which is an inference, or what a consistent set is.
Elementare Logik Göttingen 1969