*332Insofar as pertinent, the action was brought to recover a loan acknowledged by defendant in a letter that defendant claims was forged. The trial court, however, crediting plaintiffs handwriting expert, found defendant’s signature on the letter to be genuine, a finding which we see no reason to disturb. It was not reversible error to permit plaintiffs expert to remain in the courtroom during the testimony of defendant’s expert (People v Felder, 39 AD2d 373, 379-380, affd 32 NY2d 747, appeal dismissed 414 US 948). Nor was it reversible error to allow plaintiff to impeach defendant by eliciting on cross-examination the disciplinary proceedings that had been brought against him (CPLR 4513; see, People v Lee, 35 AD2d 542 [impeachment of defendant by showing dishonorable discharge from Army after court-martial held proper]). Finally, defendant’s argument that plaintiff was required to show, as part of its prima facie case, that delivery of the letter in question to plaintiff was authorized by defendant (citing UCC 3-306 [c]) was not raised at trial and therefore may not be considered on appeal. Concur—Kupferman, J. P., Milonas, Asch, Wallach and Rubin, JJ.