Researchers have known for some time that single equational axioms ( i . e ., 1-bases ) exist for Boolean algebra, including representation in terms of disjunction and negation and in terms of the Sheffer stroke.
12.
In Boolean functions and propositional calculus, the "'Sheffer stroke "', named after Henry M . Sheffer, written " | " ( see vertical bar, not to be confused with " | | " which is often used to represent Boolean algebra and digital electronics it is known as the "'NAND operation " '.
13.
This problem appears later when Wittgenstein arrives at this gentle disavowal of the axiom of reducibility one interpretation of the following is that Wittgenstein is saying that Russell has made ( what is known today as ) a category error; Russell has asserted ( inserted into the theory ) a " further law of logic " when " all " the laws ( e . g . the unbounded Sheffer stroke adopted by Wittgenstein ) have " already " been asserted:
