What proposition 6. really says is that any logical sentence can be derived from a series of NOR operations on the totality of atomic propositions. This is in fact a well-known logical theorem produced by Henry M. Sheffer , of which Wittgenstein makes use. Sheffer's result was, however, restricted to the propositional calculus, and so, of limited significance. Wittgenstein's N-operator is however an infinitary analogue of the Sheffer stroke , which applied to a set of propositions produces a proposition that is equivalent to the denial of every member of that set. Wittgenstein shows that this operator can cope with the whole of predicate logic with identity, defining the quantifiers at , and showing how identity would then be handled at -.