Is the argument A implies B, therefore A implies B or C valid?

[Ackbach]

Here is this week's POTW:

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Construct a formal proof of validity for the following argument:
\begin{align*}
A &\to B \\
\therefore A &\to (B \lor C).
\end{align*}

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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]

Re: Problem Of The Week # 200 - January 26, 2016

This is Exercise 8.21 on page 212 of Language, Proof and Logic, by Barwise and Etchemendy.

No one answered this week's POTW. Here is my solution:

Spoiler

View attachment 5217