• Sheffer’s proof that all truth-functions can be obtained out of simultaneous negation, i.e. out of “not- p and not- q ”;
• Mr. Wittgenstein’s theory of the derivation of general propositions from conjunctions and disjunctions;
• The assertion that a proposition can only occur in another proposition as argument to a truth-function. Given these three foundations, it follows that all propositions which are not atomic can be derived from such as are, by a uniform process, and it is this process which is indicated by Mr. Wittgenstein’s symbol.

Sheffer’s proof that all truth-functions can be obtained out of simultaneous negation, i.e. out of “not- p and not- q ”;

Mr. Wittgenstein’s theory of the derivation of general propositions from conjunctions and disjunctions;