Question 1171858
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I will use a conditional proof (CP). In this type of proof, we assume the 
truth of a variable and see if applying the premises leads us to the desired conclusion.  The lines of the CP are prefixed with :: and only the conclusion(s) reached from the conditional proof can be carried into the main argument. It is a subtle thing but important to keep in mind: the CP part uses info outside the CP AND also stuff already shown true inside the CP, but the non-CP part can NOT use anything except the conclusion(s) of the CP (you can't say M is true on line 10 for example, even though it is "true" on line 5 inside the CP).

1.  (Q --> ~J) --> (M --> ~D)   Premise
2.  Q --> M                     Premise
3.  M --> ~J                    Premise
:: 4.  Q             CP assumption #1
:: 5.  M             4,2 Modus Ponens (MP)
:: 6.  ~J            5,3 MP
:: 7.  Q --> ~J      4-6, CP
:: 8.  M --> ~D      7,1 MP
:: 9.  ~D            5,8 MP

10. Q --> ~D         4-9 CP

--- DONE ---


In words:
:: 4. Assume Q is true as part of the conditional proof
:: 5. M follows from premise given on line 2
:: 6. ~J follows from line 5 and line 3
:: 7. Q --> ~J   follows from lines 4 and 6 (assuming Q true, leads to ~J true)
:: 8. M --> ~D   by line 7 and premise on line 1 ... that premise says "if Q implies not J, then (M implies not D)"
:: 9. ~D is true because we have M and M implies ~D from line 8

10.  says we've shown conditionally that assuming Q true leads to ~D true (more precisely "if Q true then ~D is true"), so we can add an unconditional line to the original argument that Q --> ~D, thus completing the proof.