Section 2--202. Final Written Expression: Parol or Extrinsic Evidence.
    Terms  with respect to which the confirmatory memoranda of the parties
  agree or which are otherwise set forth in  a  writing  intended  by  the
  parties  as  a  final expression of their agreement with respect to such
  terms as are included therein may not be contradicted by evidence of any
  prior agreement or of  a  contemporaneous  oral  agreement  but  may  be
  explained or supplemented
         (a) by course of dealing or usage of trade (Section 1--205) or by
             course of performance (Section 2--208); and
         (b) by  evidence  of consistent additional terms unless the court
             finds the writing to have been intended also  as  a  complete
             and exclusive statement of the terms of the agreement.