They expect their partner will do the same for them, but it isn't an immediate quid pro quo.

WSJ: How Often Should Married Couples Have Sex?

What's more, adds Kieran Daly, editor of Air Transport Intelligence, there isn't a simple quid pro quo in terms of cabitage.

CNN: Open Skies: the bell rings for round two

Don't expect a smoking pen in the form of a blatant quid pro quo.

FORBES: Bechtel Tries To Put Iraq Back Together

While Pyongyang painted the arrangement as a quid pro quo deal, Washington said it doesn't link humanitarian aid to political matters.

WSJ: U.S. Warns North Korea Over Rocket Launch

Mr. Perez also misled Congressional investigators by saying on March 22 that he didn't have any "recollection" of using his personal email to communicate about the quid pro quo.

WSJ: Review & Outlook: The Perez Stonewall