I am struggling with natural deduction. I am doing the exercises in Fitch's book and now I am supposed to give an intelim proof of the theorem above (an intelim proof is one that uses only introduction and elimination rules and certain axioms).
I understand that it will be by implication introduction that I prove this. But I find it hard because I become entangled in the subproofs. Is this attempt below correct?
- p hypothesis
- p->(p->q) hypothesis of subproof
- p->q by 1,2, modus ponens
- p reiteration of 1
- (p->(p->q)->q by 2-5 implication introduction
Help much appreciated!