# Thread: [SOLVED] A simple SD logic derivation that is giving me fits

1. ## [SOLVED] A simple SD logic derivation that is giving me fits

I need to derive D from the following. Any help would be greatly appreciated

Premise 1: A & B
Premise 2: C -> D
Premise 3: C v ~A

2. Hello, rsportsman09!

I need to derive $D$ from the following.

. . $\begin{array}{ccc} {\color{blue}(1)} & A \wedge B \\
{\color{blue}(2)} & C \to D \\ {\color{blue}(3)} & C \:\vee \sim A \end{array}$

I'll give you the game plan ... You can supply the reasons.

From (1), $A$ and $B$ are true . . . Hence: $A$ is true. .(a)

From (3), we have: . $C \:\vee \sim A \;\;=\;\;\sim A \vee C \;\;=\;\;A \to C$ .(b)

We have: . $\begin{array}{cccc}{\color{blue}(b)} & A \to C \\ {\color{blue}(2)} & C \to D \\ & --- \\ {\color{blue}(c)} & A \to D & \text{syllogism}\end{array}$

We have: . $\begin{array}{cccc}{\color{blue}(c)} & A \to D \\ {\color{blue}(a)} & A \\ & --- \\ \therefore & D & \text{detachment}\end{array}$