17. An apparatus according to claim 16 , wherein the instructions further cause the digital processor to: compute at least one identifier selected to represent all of the statements represented by the aggregate hash; and digitally sign the aggregate hash and the at least one identifier.
16. An apparatus, comprising instructions stored on machine readable media, the instructions when executed causing a digital processor to: compute a hash of each one of multiple statements representing a graph; apply a commutative function to each of the multiple hashes to thereby yield an aggregate hash representing all of the multiple hashes; and digitally sign the aggregate hash.