Contracts II
Restatement Second of Contracts § 238
Effect on Other Party's Duties of a Failure to Offer Performance
Where all or part of the performances to be exchanged under an exchange of promises are due simultaneously, it is a condition of each party's duties to render such performance that the other party either render or, with manifested present ability to do so, offer performance of his part of the simultaneous exchange.
Copyright, The American Law Institute