 Pryde and White subsequently introduced a simplified method using intensity-symmetric multiport beam splitters, single photon inputs, and either heralded or conditional measurement.Their method, for example, allows heralded production of the "N" = 4 NOON state without the need for postselection or zero photon detections, and has the same success probability of 3/64 as the more complicated circuit of Kok et al.Cable and Dowling proposed a method that has polynomial scaling in the success probability, which can therefore be called efficient.