[Let R(n) be the n'th formula of PM [Principia mathematica], [y;z] be the substitution of z into … that n belongs to K, and let S=R(q). … [R(q);q] is not … provable.] … closely related to the "Liar" too; for the … [R(q);q] states that q belongs to K, that is, by [definition] (1), that [R(q);q] is not provable. We therefore have before … [p. 599] From the remark that [R(q);q] says about … [R(q);q] is true, for [R(q);q] is indeed unprovable (being undecidable). Thus, …
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