11. They are propositional functions, functions whose values are truth values . 12. NULL = NULL ) return a truth value of Unknown. 13. Instead they remain of unknown truth value , until they are either proved or disproved. 14. In particular, truth value and mythological status are separate issues. 15. Ordinarily, coreferring names are substitutable salva veritate, that is, without change in truth value . 16. In classic logic, connectives are defined according to truth values . 17. :The statement is not about anything in particular, so it has no truth value . 18. This might result in a totally flat truth-theoretic framework, or even arbitrary truth values . 19. RRA thus formalizes and clarifies " LoF "'s notion of an imaginary truth value . 20. Note that " mu " is standard fuzzy-logic nomenclature for " truth value ":
