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The Collaborative International Dictionary
Counterproving

Counterprove \Coun`ter*prove"\ (koun`t?r-pr??v"), v. t. [imp. & p. p. Counterproved (-pr??vd"); p. pr. & vb. n. Counterproving.] To take a counter proof of, or a copy in reverse, by taking an impression directly from the face of an original. See Counter proof, under Counter.

Wiktionary
counterproving

vb. (present participle of counterprove English)