document.write( "Question 1056542: prove validity using inference rules and rules of replacement and say which rule was used at each step:
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\n" ); document.write( " 1. {X+[Y+(~(A.F)>B)]}
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\n" ); document.write( " 4. {~B.[Z.(~C+~C)]}
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\n" ); document.write( " 1. (A+C)+(A+B)
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\n" ); document.write( " 1. (A>C)+(B>D)
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Algebra.Com's Answer #671645 by Edwin McCravy(20056)\"\" \"About 
You can put this solution on YOUR website!
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document.write( "Unless your teacher tells you otherwise, do not number\r\n" );
document.write( "the conclusion [what follows the \"/\"] until the end.\r\n" );
document.write( "It should be written out to the right of the last given \r\n" );
document.write( "premise.  At least, that's the way logic is normally \r\n" );
document.write( "taught.\r\n" );
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document.write( "1.	X+[Y+(~(A•F) ⊃B)]\r\n" );
document.write( "2.	X⊃C\r\n" );
document.write( "3.	Y⊃C\r\n" );
document.write( "4.	~B•[Z•(~C+~C)]    /F•Z\r\n" );
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document.write( "6.      Z•(~C+~C)              4, simp.\r\n" );
document.write( "7.      Z•(~C)                 6, taut.\r\n" );
document.write( "8.      Z                      7, simp.\r\n" );
document.write( "9.      ~C•Z                   7, comm.\r\n" );
document.write( "10.     ~C                     9, simp.\r\n" );
document.write( "11.     ~X                     2,10, MT  \r\n" );
document.write( "12.     ~B                     4, simp.\r\n" );
document.write( "13.     Y+(~(A•F)⊃B)           1,11, DS\r\n" );
document.write( "14.     Y+{[~B⊃(~~(A•F)]}      13, trans.\r\n" );
document.write( "15.     Y+[~B⊃(A•F)]           14, DN\r\n" );
document.write( "16.     ~Y                     3,10, MT        \r\n" );
document.write( "17.     ~B⊃(A•F)               15,16, DS\r\n" );
document.write( "18.      A•F                    17,12, MP\r\n" );
document.write( "19.      F•A                    18, comm.\r\n" );
document.write( "20.      F                      19, simp.\r\n" );
document.write( "21.      F•Z                    20,8, conj.\r\n" );
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document.write( "-----------------------------------------\r\n" );
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document.write( "1. (A+C)+(A+B)\r\n" );
document.write( "2. (A+(B+C))⊃D      /D \r\n" );
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document.write( "3. A+[C+(A+B)]                  1, Assoc.\r\n" );
document.write( "4. A+[(A+B)+C]                  3, Comm.  \r\n" );
document.write( "5. [A+(A+B)]+C                  4, Assoc.\r\n" );
document.write( "6. [(A+A)+B]+C                  5, Assoc.\r\n" );
document.write( "7. (A+B)+C                      6, taut.\r\n" );
document.write( "8. A+(B+C)                      7, Assoc.\r\n" );
document.write( "9. D                            2,8, MP   \r\n" );
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document.write( "Two problems is the limit.\r\n" );
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document.write( "Edwin
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