Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:In state of the art schemes [16,5], a warrant ω is either the concatenation of all permitted messages or an abstract description of the message space for which signing is being delegated, together with a certificate, which is a signature on ω (and typically other values including the proxy’s identity and public key), under the delegator’s private signing key.
Category: