Section 3018. Responsive pleadings

(a) Denials. A party shall deny those
  statements known or believed by him to be untrue. He shall specify those
  statements as to the truth of which he lacks  knowledge  or  information
  sufficient  to form a belief and this shall have the effect of a denial.
  All other statements of a pleading  are  deemed  admitted,  except  that
  where  no  responsive  pleading  is  permitted they are deemed denied or
  avoided.
    (b) Affirmative defenses. A party shall plead all matters which if not
  pleaded would be likely to take the adverse party by surprise  or  would
  raise  issues of fact not appearing on the face of a prior pleading such
  as arbitration and award, collateral estoppel, culpable conduct  claimed
  in  diminution  of damages as set forth in article fourteen-A, discharge
  in bankruptcy, facts showing illegality either by statute or common law,
  fraud, infancy or other disability  of  the  party  defending,  payment,
  release,  res judicata, statute of frauds, or statute of limitation. The
  application of this subdivision shall not be confined to  the  instances
  enumerated.