document.write( "Question 1188425: Formal proof: In the text box below, use the proof method (M9) to construct a formal proof to demonstrate that the following argument is valid: \r
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Algebra.Com's Answer #821047 by Edwin McCravy(20055)\"\" \"About 
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document.write( " 1. (A • B) ⊃ (E ⊃ A)\r\n" );
document.write( " 2. (A • B) v C\r\n" );
document.write( " 3. C ⊃ D                /.: (E ⊃ A) v D\r\n" );
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document.write( "                  |4. ~[(E ⊃ A) v D]         Assumption for Indirect Proof\r\n" );
document.write( "                  |5. ~(E ⊃ A) • ~D                     4, DeMorgan's law   \r\n" );
document.write( "                  |6. ~D • ~(E ⊃ A)                     5, Commutation\r\n" );
document.write( "                  |7. ~D                                6, Simpliofication\r\n" );
document.write( "                  |8. ~C                                3,8, Modus Tollens    \r\n" );
document.write( "                  |9. C v (A • B)                       2, Commutation\r\n" );
document.write( "                 |10. A • B                             9,8, Disjunctive syllogism \r\n" );
document.write( "                 |11. E ⊃ A                            1,10, Modus ponens\r\n" );
document.write( "                 |12. (E ⊃ A) v D                       11, Addition\r\n" );
document.write( "                 |13. [(E ⊃ A) v D] • ~[(E ⊃ A) v D]   12,4, Conjunction            \r\n" );
document.write( "14. E ⊃ A) v D        Lines 4-13              Indirect Proof\r\n" );
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document.write( "Edwin
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