Colfax (P) manufacturer envelopes. It also prints them, and the seventeen employees who do the printing are represented by LOCAL NO. 458-3M (D). P does not bother to participate in the collective bargaining negotiations between D and the Chicago Lithographers Association. Whenever D and the CLA sign a new collective bargaining agreement, the union sends P a summary of the changes that the new agreement has made in the old one which P signs and returns. If P doesn't like the terms negotiated by the CLA, it is free to do its own bargaining with D. In 1991 D sent a summary of the changes to P. The changes indicated that all presses operated as four-color presses would now require only three men to man them. P accepted the terms in the summary. When the actual agreement arrived, it contained a crucial typo, which supported P's understanding of the summary. When a corrected copy of the agreement finally arrived, the manning requirements stated in it were different from what P had understood from the summary. Four-color presses between 45 and 60 inches required three men, but all four-color presses over 60 inches required four men. P refused to sign the agreement, but D took the position that P was bound to it by its acceptance of the summary. P sued for a declaration that it has no collective bargaining contract D because the parties never agreed on an essential term--the manning requirements for P's printing presses. D counterclaimed for an order to arbitrate. The district judge granted summary judgment for D, concluding that the reference to the new manning requirement for a four-color 60-inch press in the summary of changes that P had accepted referred unambiguously to 60-inch presses and had no application to any other presses, such as P's 78-inch presses. P appealed.