P sued D alleging a breach of contract to wit; D failed to take and pay for 800 tons of corrugated materials per month. A written contract was signed between the parties that stated that D would buy 600 tons more or less. The court determined the contract to be unambiguous and parol evidence could not be used to vary the terms. D was given the judgment. P then filed a reformation suit. D moved for summary judgment based on res judicata. It was granted. P appealed.