1. A computer implemented method for determining whether a rule R is redundant with respect to a rule set S containing a plurality of non-redundant rules each defining tests of varying type for performing on a corresponding numeric field in a packet P of fields (p 1,... p n ) such that each field is associated with a specific type of test, which may be blank, such that the intersection of two intersecting rules is a rule and wherein the packet P satisfies a rule if each field satisfies the corresponding test in the rule or if the corresponding test is blank, said method comprising: (a) generating a new rule set S′ containing for each rule R i in S its intersection with R (R i ) where R and R i, intersect; and (b) determining that the rule R is redundant with respect to the rule set S if an equal number of packets satisfies R and the union of all rules in S′.