1. A concurrent processing method in an information processing system having a plurality of processors and a shared memory which is shared by said processors, the method comprising: a step of setting n each of said plurality of processors one of a plurality of matching algorithms for deriving a matching results for each of the plurality of matching algorithms, which algorithms are expected to derived a same matching result form an input knowledge representation which is input concurrently into the matching algorithms, said plurality of matching algorithms including at least two of a RETE matching algorithm, a TREAT matching algorithm, and an XC matching algorithm; a step of parallel processing, as an inference cycle, said input knowledge representation concurrently with each of said matching algorithms, such that one of said matching algorithms derives the same matching result first; and, a step of outputting, as an output of said inference cycle, the same matching result of said one of the matching algorithms which derived the same matching result first.