SOLUTION: Please solve using natural deduction (only rules of implication + rules of replacement). Thx! 1. A ⊃ U / A ⊃ (K ⊃ U)

This one involves material implication 
P ⊃ Q is equivalent to ~P v Q


1. A ⊃ U
           / A ⊃ (K ⊃ U)

2. ~A v U           1, Material implication
3. ~A v (U v ~K)    2, Addition  
4. ~A v (~K v U)    3, Commutation
5. A ⊃ (~K v U)     4, Material implication
6. A ⊃ (K ⊃ U)      5, Material implication

Edwin