His claim is clearly absurd. Your decision MUST BE AN ECONOMICAL/BUSINESS one. I suggest you not take it personally. Weigh the cost of retaining an attorney (which you should) vs. negotiating a settlement IF POSSIBLE. If that isn't possible, let him prove his case and you defend the claim.
If you give me your state and nearest large city, I will get you a link to a directory we lawyers use to find highly qualified legal specialists in various fields at locations world wide. These lawyers are in the directory because they were rated as qualified by other lawyers in their field of expertise and geographic area.
Here you go:
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