11. With the advent of algebraic logic it became apparent however that classical propositional calculus admits other semantics. 12. Propositional calculus restricts attention to abstract propositions, those built up from propositional variables using Boolean operations.13. This can shown as follows : Every proof in propositional calculus uses only axioms and the inference rules. 14. Truth-functional propositional calculus is a formal system whose formulae may be interpreted as either true or false. 15. Schwartz ( 1981 ) proved that the " pa " is equivalent-- classical propositional calculus . 16. Sheffer's result was, however, restricted to the propositional calculus , and so, of limited significance. 17. A little more of my efforts do survive in the complex of articles concerned with propositional calculus and truth tables. 18. In particular, checking whether T entails F in this condition can be done using the rules of the propositional calculus . 19. This motivated me to ask the question : Is propositional calculus and logic the core content of formal or mathematical logic? 20. In this sense, it is a meta-theorem, comparable to theorems about the soundness or completeness of propositional calculus .
