Refer to Helena C's ref. material.

Promesa > literally a promise, but also an undertaking or covenant. In this context, speculatively a unilaterally binding option.

I think "promise" is self explanatory. "Future" would seem to be as well.

I think what your looking for is "mixed swap," a subset of security-based swap s that are based on the value of 1 or more interest or other rates, currencies, commodities, instruments of indebtedness, indices, quantitative measures, other financial or economic interest or property of any kind.

You can see this description on page 10 (of the PDF) of the first web reference, footnote 10.

It follows that they would be a promise to perform a mixed swap in the future.

And just to note:

This is not an option. Options are just that, an option to buy or sell something. It is not an agreement, which is binding.

promesa obligacional=binding promise (agreement)
promesa de permuta=promise of barter agreement
mixta=mixed (goods and services)

http://definitions.uslegal.com/b/barter/
https://www.uclm.es/profesorado/mcgonzalez/pdf/ConstruccionV...



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Note added at 4 hrs (2014-06-24 18:20:49 GMT)
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Explanation of why I use PROMISE:

Definition of legal term PROMISE: The manifestation of an intention to act or refrain from acting in a specified manner, conveyed in sucha a way that another is justified in understanding that a commitment has been made. BINDING PROMISE: a binding promise -one that the law will enforce- is the essence of a contract (Black´s)

Examples of usage in contract law:

http://books.google.com.ar/books?id=L0csAwAAQBAJ&pg=PA7&lpg=...

https://mises.org/document/1951/A-Libertarian-Theory-of-Cont...


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Note added at 22 hrs (2014-06-25 12:45:11 GMT)
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Explanation of BARTER/BARTERING:

Barter is the trading of goods or services directly for other goods or services, without using money or any other similar unit of account or medium of exchange. (http://definitions.uslegal.com/b/barter/)

While most people barter without an agreement, this can backfire down the line. On the one hand, like every contract, having the exchange on paper, signed by the parties involved, means everyone has to keep up their end of the bargain. (https://www.rocketlawyer.com/document/barter-agreement.rl)

PERMUTA: Permuta
Contrato, llamado también de permutación o
de trueque, que tiene lugar cuando uno de los
contratantes se obliga a transferir a otro la propiedad
de una cosa, a cambio de que éste le dé
la propiedad de otra. Claro es que la cosa dada
en trueque o permuta nunca puede ser dinero,
porque entonces se estaría frente a un contrato
de compraventa. (...) (Diccionario jurídico Ossorio)