What is a dog’s exchange? If one says to his fellow, “Take this lamb in exchange for this dog.” Similarly, [if] two partners divided [their animals between them], one took ten [lambs] and one took nine [lambs] and a dog, [the lambs] that are [taken] against the dog are prohibited, [while those] that are [taken] with the dog are permitted.  A dog’s wage and a harlot’s exchange, these are permitted, as it is stated: “two,” and not four. The offspring [of an esnan and of a mechir kelev] are permitted, as it is stated: “they,” and not their offspring.