### Question Description

I’m working on a philosophy question and need guidance to help me learn.

*Directions**: U**se** the proof method (M_{9}) to construct a formal proof to demonstrate that the following argument is valid:*

A ⊃ B, B ⊃ C, C ⊃ D /∴ A ⊃ ~(~C v ~D)

*In the space below, either (OPTION 1) type your completed proof or (OPTION 2) upload a photo or screenshot of your handwritten completed proof.*

**OPTION 1**: Type your formal proof. To do this, first, copy and paste the argument, set up the proof, then make inferences until you deduce the conclusion. To the right of each inference, identify the line number(s) from which it was deduced and the abbreviation of the rule of natural deduction used to make the inference. You can copy and paste any of the following symbols as needed:2 attachmentsSlide 1 of 2

- attachment_1attachment_1
- attachment_2attachment_2

### UNFORMATTED ATTACHMENT PREVIEW

11 Conditional proofs and Indirect proofs “The success of democracy depends, in the end, on the reliability of the judgments we citizens make, and hence upon our capacity and determination to weigh arguments and evidence rationally.” – Irving M. Copi STUDENT LEARNING OUTCOMES • Know what an assumed premise (AP) is and how to make one within a formal proof.. • Know the two ways an assumed premise may be discharged, how to do so, and what may be inferred and added to a proof when an assumed premise is discharged • Know how to use conditional proof rule (CP) to deduce a conditional within a formal proof. • Understand why a conditional deduced via CP is guaranteed to be true. • Know how to use indirect proof rule (

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