Computer Science 2209A/B Lecture Notes - Lecture 9: Informal Logic, Metalanguage, Ion
3 Apr 2017
School
Department
Course
Professor
Document Summary
We have seen how to prove arguments valid by using truth tables and other semantic methods. We now want to replace this approach by a purely syntactic one, that is, we give formal rules for deduction which are purely syntactical. We want to de ne a relation called formal deducibility to allow us to mechanically check the validity of a proof. The signi cance of the word formal will be explained later. The important point is that formal deducibility is concerned with the syntactic structure of formulas and proofs can be checked mechanically. Suppose = fa1; a2; a3; : : : g. For convenience, may be written as a sequence. The sets [ fag and [ 0 may be written as ; a and ; 0 respectively. We use the symbol a to mean that a is formally deducible (or provable) from.
