A General Method in Proofs of Undecidability In Undecidable Theories (1953) by Alfred Tarski edited by Alfred Tarski, Andrzej Mostowski, Raphael M. Robinson

@incollection{tarski-1953, address = {Amsterdam}, author = {Tarski, Alfred}, booktitle = {Undecidable Theories}, chapter = {1}, editor = {Tarski, Alfred and Mostowski, Andrzej and Robinson, Raphael M.}, keywords = {decidability, logics, math}, posted-at = {2014-01-08 11:25:37}, priority = {2}, publisher = {North-Holland Publishing Co.}, title = {A General Method in Proofs of Undecidability}, year = {1953} }

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A model is a substitution of variables in a theory by objects (individuals) which satisfies all the theory's sentences.⇒