This Guaranty Agreement and each Guaranty Joinder Agreement, together with the Credit Agreement and other Loan Documents, constitutes and expresses the entire understanding between the parties hereto with respect to the subject matter hereof, and supersedes all prior negotiations, agreements, understandings, inducements, commitments or conditions, express or implied, oral or written, except as herein contained.  The express terms hereof control and supersede any course of performance or usage of the trade inconsistent with any of the terms hereof.  Except as provided in Section 21 , neither this Guaranty Agreement nor any Guaranty Joinder Agreement nor any portion or provision hereof or thereof may be changed, altered, modified, supplemented, discharged, canceled, terminated, or amended orally or in any manner other than as provided in the Credit Agreement.