— Judgment, Supreme Court, New York County, entered September 28, 1979, which, inter alia, granted the petition to vacate an arbitration award, unanimously reversed, on the law, with costs and disbursements, the petition dismissed, and the cross motion to confirm granted. Contrary to Special Term’s finding, the arbitrator’s determination that there was a transfer of operations, rather than a plant closing within the intended application of the severance pay provision of the collective bargaining agreement, was not irrational. The construction of the collective bargaining agreement was a function of the arbitrator, not the court. Nor did the arbitrator exceed his authority by admitting parol evidence as to the intention of the parties with respect to the severance pay provision. "Absent provision to the contrary in the arbitration agreement, arbitrators are not bound by principles of substantive law or rules of evidence”. (Matter of Associated Teachers of Huntington v Board of Educ., 33 NY2d 229, 235, citing Lentine v Fundaro, 29 NY2d 382, 385, and cases there cited.) Moreover, and in any event, the parol evidence rule has no application to a subsequent agreement, and the rule does not exclude parol evidence of a subsequent modification or discharge of a written agreement. (Haight v Cohen, 123 App Div 707.) Concur — Sandler, J. P., Sullivan, Bloom, Silver-man and Ross, JJ.