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This step is not the source of the fallacy.

This step is establishing notation, saying what the symbol y is going to be used for in this proof.

This is a perfectly legitimate thing to do, since y does not yet have a meaning assigned to it.

Why don't you go back to the list of steps in the proof and see if you can identify which one is wrong, now that you know it isn't this one?
This page last updated: May 26, 1998
Original Web Site Creator / Mathematical Content Developer: Philip Spencer
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