bill of proof

from Bouvier's Law Dictionary, Revised 6th Ed (1856)
BILL OF PROOF. In the mayor's court, London, the claim made by a third 
person to the subject-matter in dispute between two others in a suit there, 
is called bill of Proof. It is somewhat similar to an intervention. (q. v.) 
3 Chit. Com. Law, 633; 2 Chit. Pr. 492; 1 Marsh, R. 233. 
    

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