The PISA output was processed using version 2.3 of PISORP which was modified slightly so that all subevents in which one or more hits occur in the third tracking station could be discarded if any such hit is produced by track number two and the particle producing the hit is a muon. Since the PISA runs were comprised of single-particle-events, primary particles all had track number = 1 and muons produced by the decay of a primary pion always had track number = 2. Using this scheme all decay muons were removed from the pion data except for primary pions that decayed after traversing the third tracking station. The simulation procedure is shown schematically in Fig. 1.