 On one fairly standard interpretation, the later Wittgenstein says that “true in calculus \(\Gamma\)” is identical to “provable in calculus \(\Gamma\)” and, therefore, that a mathematical proposition of calculus \(\Gamma\) is a concatenation of signs that is either provable (in principle) or refutable (in principle) in calculus \(\Gamma\) (Goodstein 1972: 279, 282; Anderson 1958: 487; Klenk 1976: 13; Frascolla 1994: 59). On this interpretation, the later Wittgenstein precludes undecidable mathematical propositions, but he allows that some undecided expressions are propositions of a calculus because they are decidable in principle (i.e., in the absence of a known, applicable decision procedure).