|Tractatus Logico-Philosophicus by Ludwig Wittgenstein + comments by Maarten Maartensz|
What is true is that the value of a truth-function of p is a function of the value of p - and whether the same applies to meaning or sense is doubtful. A more precise sense in which "Negation, logical addition, logical multiplication, etc. etc. are operations. (Negation reverses the sense of a proposition.)" can be taken from my last remark, with a formal statement of binary Boolean Algebra.