[離散數學]四版習題10-65

65.Construct a formal proof the following theorem:
if (P or R) and(Q or R'),then(P or Q)
不知可否這樣解
SOL:
題目等價 [ (P'=>R) and (R=>Q) ] =>(P or Q)
把它變成一個推理問題
(P'=>R)
(R=>Q)
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所以(P or Q)

因為=>具遞移性
所以 P'=>R and R=>Q
=>P'=>Q
=>P or Q 得証