facio ut facias

from Bouvier's Law Dictionary, Revised 6th Ed (1856)
FACIO UT FACIAS. A species of contract in the civil law, which occurs when I 
agree with a man to do his work for him if he will do mine for me. Or if two 
persons agree to marry together, or to do any other positive acts on both 
sides. Or it may be to forbear on one side in consideration of something 
done on the other. 2 Bl. Com. 444. 
    

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