the execution of the agreement depend on an event which it is in the power of the one or the other of the contracting parties to bring about or to hinder. Civ. Code La. art. 2024

They are either erpress or implied, the former when incorporated in express terms in the deed, contract, lease, or grant; the latter, when inferred or presumed by law, from the nature of the transaction or the conduct of the parties, to have been tacitly understood between them as a part of the agreement, though not expressly mentioned. 2 Grabb, Real Prop. p. 792; Bract. fol. 47; Civ. Code La. art. 2026;

the second class ‘when the performance of one condition is not obligatory until the actual performance of the other; and to the third class when neither party need perform his condition uniess the other is ready and willing to perform his, or, in other words, when the mutual covenants go to the whole consideration on both sides and each is precedent to the other. Huggins v. Daley, 99 Fed. 609, 40 C. C.