1. A data processing system to enable the formulation of multi-party investment contracts, the system comprising: input means by which an ordering party can input contract data relating to at least one phenomenon, each said phenomenon having a range of future outcomes and a future time of maturity, the contract data including a set of probabilities of occurrence for each outcome in said range and a consideration due to a counterparty at or after the time of matching, and further by which at least one counterparty can input registering data including a set of probabilities of occurrence for each outcome in said range; and data processing means operable to price and match a contract for a said phenomenon from said contract data and said registering data, the pricing including: applying at least one template of entitlement as a function of outcome to each counterparty's set of probabilities to give one or more individual counterparty prices each equal to the ordering party's consideration; and applying the ordering party set of probabilities to each said template of entitlement to derive an implied entitlement valuation; the matching including: determining which counterparty will provide the best entitlement on maturity by comparing each implied entitlement valuation with the consideration; and matching the contract with that counterparty having a template of entitlement for the best said comparison.