1. P—>A Premise 2. X—>B Premise 3. (P v X) —> (A v B) This follows directly by Constructive Dilemma (CD) =================================== I think this proves it the long way… — 1. P—>A Premise 2. X—>B Premise 3. P v X Premise ::4. P Assumption, start Conditional Proof (CP) ::5. A 4,1 Modus Ponens (MP) ::6. A v B 5 Addition (ADD) ::7. X Assumption ::8. B 7,2 MP ::9. A v B 8 ADD 10. A v B 1,2,3 Proof By Cases (PBC) { Discharges CP assumptions } 11. (P v X) —> (A v B) 1,2 CP