CST329 - Module 4

What did I learn in the fourth week of CST329? 

This module covered chapters 8, 9, and 10. Chapter 8 introduced reductio ad absurdum, a rule that can prove a sentence by assuming its denial, deriving a contradiction, and then finishing the subproof with a indirect derivation. Chapter 9 introduced biconditional along with two new rules, which were equivalence and bicondition. Equivalence is used when taking away for either of the two sides in <->, while bicondition combines two conditionals in opposite directions with <->. Furthermore, this chapter covered theorems and how they can be cited directly in later proofs, while also illustrating how substituting sentences for atomic letters in a theorem can still produce a theorem. Lastly, chapter 10 was a summary of what we have learned throughout all the chapters so far, going over propositional logic, principle of bivalence and tautologies, contradictions, and contingent sentences.

Across these three chapters, I worked through practice problems and homework using Proof Checker to construct proofs involving reductio ad absurdum, prove biconditional theorems using bicondition and equivalence, identify legal instantiations of the ten listed theorems (T1–T10), and classify sentences as tautologies, contradictory sentences, or contingent sentences based on their truth tables.