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Symbolic Logic Problem

I have to determine whether or not this formal argument below is valid. If it is I have to provide a derivation of the conclusion from the premises, which I don't know how to do. If it is invalid, an interpretation which shows the invalidity must be constructed. The & signs mean "and" usually signified by a dot. The asterisk signifies a conditional (usually signified by an arrow).

(X)((LX&DX)* FX)
(EX)(DX&~FX)
__________________
~(EX)LX

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Invalid:

let ...

Solution Summary

A symbolic logic expression is proven to be invalid.

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