What is the legal principles in this case? Harris N. Dealer was sole proprietor of a profitable computer data centre, which he sold as a going concerto Alice B. Wheeler for the price of $180,000. The price was paid - $30,000 in cash and the balance in the form of a contract under Wheeler's seal, which read in part a follows: For value received Alice B. Wheeler promises to pay Harris N. Dealer the sum of one hundred and fifty thousand dollars ($150,000) in 10 years from April 1st, 2009, together with interest at 8% per annum from April 1, 2009, payable monthly on the first of May 2009 and on the first day of each and every month thereafter until payment of the principal sum on April 1,2019. After ten (10) days default in any interest payment due under this agreement the whole amount payable shall become immediately due. Dealer and Wheeler remained on friendly terms throughout the balance of 2009, Wheeler was somewhat dilatory in making her monthly payments of $1,000 interest, so that by the end of the year she had made six of the eight monthly payments required by them on dates more than 10 days after they were due. Dealer had acquiesced in the arrangement without complaint, though the parties had never expressly agreed on any change in the due dates and Dealer seemed merely to have been indulgent with his debtor. Unfortunately, however, the parties had a serious personal disagreement early in 2010. On February 05,2010, the January 1st interest payment then being 35 days overdue, Dealer wrote to Wheeler as follows: This letter will serve to inform you that, an interest payment due under the terms of the contract dated March 29th,2009, being in default for more than 10 days, the whole amount under the contract is now due. I hereby demand immediate payment of the principal amount of $150,000 and outstanding interest