Further help with Reductio

Sentential Logic: 10 Tutorials
 Tutorial 1 Introduction, sketch of course, and symbolizing atomic sentences.
 Tutorial 2: Symbolizing compound sentences
 Review
 Tutorial 3: Sentences and Truth
 Tutorial 4: Arguments and searching for a counter example
 Review 2
 Tutorial 5: Valid arguments, searching for a proof
 Tutorial 6: What is a derivation and what does it prove? How experts do derivations.
 Tutorial 7: Conditional Proof
 Tutorial 8: Reductio ad Absurdum
 Tutorial 9: The Remaining Sentential Rules of Inference
 Tutorial 10: Common Inference Patterns and Rewrite Rules
 Review of Sentential Logic
 Sentential Logic: Try your own derivations
 Predicate Logic: 15 Tutorials