Consider the following reduction ad absurdum proof in propositional logic. the justification lines (to the right) are missing. fill in the blanks. 1. a ⊃ ~b premise 2. ~b ⊃ (c . b) premise 3. ~c v ~b premise 4. a premise / show x 5. ~x assumption for purposes of indirect proof 6. ~b 7. ~(c . b) 8. b 9. ~a 10. a . ~a 11. ~x ⊃ (a . ~a) 12. ~ (a . ~a) 13. x 4,2 mp; 3 dm; 7,2 mt; 8,1 mt; 4, 9 conj.; 6-11 indirect proof; nc; 5,13 mt 3,1 mp; 3 dm; 6,2 mt; 8,1 mp; 4, 9 conj.; 5-11 indirect proof; nc; 12,13 mt 4,1 mp; 3 dm; 7,2 mt; 8,1 mt; 4, 9 conj.; 5-10 indirect proof; nc; 11,12 mt 4,1 mp; 3 dm; 7,2 mt; 7,1 mt; 4, 9 add.; 5-11 indirect proof; conj; 12,1