facio ut des

from Bouvier's Law Dictionary, Revised 6th Ed (1856)
FACIO UT DES. A species of contract in the civil law, which occurs when a 
man agrees to perform anything for a price, either specifically mentioned or 
left to the determination of the law to set a value on it. As when a servant 
hires himself to his master for certain wages or an agreed sum of money. 2 
Bl. Com. 445. 
    

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