MHB Can you prove $C\lor D$ using given premises?

[Ackbach]

Here's this week's problem.

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From $A\lor B, \; A \to C, \; \neg D \to \neg B$, prove
$C\lor D$. You may use any valid first-order deduction system, but you
must indicate which one you are using (Copi's 19 Rules, Natural
Deduction, etc.).

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Remember to read the http://www.mathhelpboards.com/showthread.php?772-Problem-of-the-Week-%28POTW%29-Procedure-and-Guidelines to find out how to http://www.mathhelpboards.com/forms.php?do=form&fid=2!

 

[Ackbach]

No one answered this week's Undergraduate POTW; I was hoping this problem could at least tempt Evgeny! ;)

Here is my answer:

Spoiler

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