Bill Simpich, State Secret, Chapter 4, Mexico City Intrigue - The Wold Of Surveillance: https://www.maryferrell.org/pages/State_Secret_Chapter4.html
"Why two tap operations? LIENVOY and LIFEAT were known within the Agency as ZRJOINT and ZRSOLO. It’s pretty clear why. LIENVOY was a joint operation with the DFS. LIFEAT, on the other hand, was strictly a US affair insulated from DFS scrutiny."
"There is one qualification which the Chief of Station expects in his reports officers, and in most of his case officers as well, and that is a good working knowledge of Spanish. The transmission of the Spanish language take from the ZRJOINT intercept center and the ZRSOLO listening posts is not delayed by translation, like the product of the Czech, Polish and Yugoslav lines, which stays one day with the various translators."