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document.write( "Give reasons for the steps, given premises 1, 2 and 3:\r\n" );
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document.write( "1.  X ⊃ (Y ⊃ Z)\r\n" );
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document.write( "2.  X ⊃ (A ⊃ B)\r\n" );
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document.write( "3.  X • (Y ∨ A)     ∴  ∼B ⊃ X \r\n" );
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document.write( "4.  X                   \r\n" );
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document.write( "5.  A ⊃ B          \r\n" );
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document.write( "6.  Y ⊃ Z           \r\n" );
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document.write( "7.  (Y ∨ A) • X    \r\n" );
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document.write( "8.  Y ∨ A              \r\n" );
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document.write( "9. ∼(∼Y) ∨ A       \r\n" );
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document.write( "10. ∼Y ⊃ A          \r\n" );
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document.write( "11. ∼Y ⊃ B         \r\n" );
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document.write( "12. ∼B ⊃ ∼(∼Y)  \r\n" );
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document.write( "13. ∼B ⊃ Y          \r\n" );
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document.write( "14.  X ∨ ∼Y         \r\n" );
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document.write( "15.  ∼Y ∨ X        \r\n" );
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document.write( "16.  Y ⊃ X           \r\n" );
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document.write( "17. ∼B ⊃ X     \r\n" );
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Algebra.Com's Answer #732606 by Edwin McCravy(20055)\"\" \"About 
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document.write( "Give reasons for the steps, given premises 1, 2 and 3:\r\n" );
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document.write( "1.  X ⊃ (Y ⊃ Z)\r\n" );
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document.write( "2.  X ⊃ (A ⊃ B)\r\n" );
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document.write( "3.  X • (Y ∨ A)     /∴  ∼B ⊃ X \r\n" );
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document.write( "4.  X                 3, Simplification\r\n" );
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document.write( "5.  A ⊃ B           2,4, Modus Ponens\r\n" );
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document.write( "6.  Y ⊃ Z           1,4, Modus Ponens\r\n" );
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document.write( "7.  (Y ∨ A) • X       3, Commutation\r\n" );
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document.write( "8.  Y ∨ A             7, Simplification \r\n" );
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document.write( "9. ∼(∼Y) ∨ A          8, Double Negation\r\n" );
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document.write( "10. ∼Y ⊃ A           10, Material Implication\r\n" );
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document.write( "11. ∼Y ⊃ B         10,5, Hypothetical Syllogism\r\n" );
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document.write( "12. ∼B ⊃ ∼(∼Y)       11, Transposition\r\n" );
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document.write( "13. ∼B ⊃ Y          12, Double Negation\r\n" );
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document.write( "14.  X ∨ ∼Y           4, Addition\r\n" );
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document.write( "15.  ∼Y ∨ X          14, Commutation\r\n" );
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document.write( "16.  Y ⊃ X           15, Material Implication\r\n" );
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document.write( "17. ∼B ⊃ X        13,16, Hypothetical syllogism\r\n" );
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document.write( "Edwin
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