The Printers Union reached agreement on a new 3 year contract with a large regional printing company. Sullivan Brothers Printers is a small printing company whose employees were represented by the Printers Union. It was the practice of the company to follow the agreements made by larger companies with the Union; this is called pattern bargaining. Sullivan Brothers agreed to all of the benefits negotiated by the larger companies. When the contract was typed it left out a provision which required the company to pay 75% of the premium costs of a dental plan and the contract was signed without that provision in it. Six months after the contract was signed the omission was discovered. Sullivan brothers contend the signed document should be followed. The Union contends the evidence shows a typing error. Decide the case.