1. A computer trading system, comprising: one or more computer systems storing a set of information indicative of credit relationships between a plurality of trading entities, wherein the plurality of trading entities includes a first trading entity, a second trading entity and a third trading entity, each of which is different, wherein the set of information indicates that a first credit path exists between the first and second trading entities, wherein the first credit path includes the third trading entity; wherein the one or more computer systems store program instructions executable by the one or more computer systems to cause the one or more computer systems to: receive a first proposal to trade from the first trading entity; compute a second proposal to trade for the second trading entity based on the first proposal to trade and based on a current amount of credit available to the second trading entity over the first credit path; and convey a limit order book to the second trading entity, wherein the limit order book includes the second proposal to trade.