1. P ⊃ ~M
2. C ⊃ M
3. ~L v C
4. (~P ⊃ ~E) • (~E ⊃ ~C)
5. P v ~P /~L
6. (~E ⊃ ~C) • (~P ⊃ ~E) 4, commutation
7. ~E ⊃ ~C 6, simplification
8. ~~C ⊃ ~~E 7, transposition
9. C ⊃ E 8, double negation
10. ~P ⊃ ~E 4, simplification
11. ~~E ⊃ ~~P 10, transposition
12. E ⊃ P 11, double negation
13. C ⊃ P 9,12 hypothetical syllogism
14. C ⊃ ~M 13,1, hypothetical syllogism
15. ~M ⊃ ~C 2, transposition
16. C ⊃ ~C 14,15, hypothetical syllogism
17. ~C v ~C 16, material implication
18. ~C 17, tautology
19. C v ~L 3, commutation
20. ~L 19,18, disjunctive syllogism
Edwin