document.write( "Question 1188428: Use natural deduction to prove the following logical truth:
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Algebra.Com's Answer #838334 by RBryant(14)\"\" \"About 
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document.write( "// [F • (D ⊃ ∼ F)] ⊃ (D ⊃ A)    \r\n" );
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document.write( "1.     [F • (D ⊃ ∼ F)] ⊃ (D ⊃ A)             Assumption\r\n" );
document.write( "2.         [F • (D ⊃ ∼ F)]                    Assumption\r\n" );
document.write( "3.              D                              Assumption\r\n" );
document.write( "4.              F                              2              & Intro \r\n" );
document.write( "5.              D ⊃ ~F                         2              & Intro\r\n" );
document.write( "6.              ~F                             3,5            ⊃ Elim \r\n" );
document.write( "7.              F • ~F                         4,6            & Intro\r\n" );
document.write( "8.           A                                 7              Falsum Intro\r\n" );
document.write( "9.      D ⊃ A                                 3-8             ⊃ Intro\r\n" );
document.write( "10.  [F • (D ⊃ ∼ F)] ⊃ (D ⊃ A)               2-9             ⊃ Intro\r\n" );
document.write( "                                                                        QED\r\n" );
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