pactum de quota liti

from Bouvier's Law Dictionary, Revised 6th Ed (1856)
PACTUM DE QUOTA LITIS. An agreement by which a creditor of a sum difficult 
to recover, promises a portion, for example, one-third, to the person who 
will undertake to recover it. In general, attorneys will abstain from, 
making such a contract, yet it is not unlawful. 
    

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