Romer, H.F.; Chase, R.C.; Coleman, E.; Courant, H.W.J.; Marquit, E.; Petraske, E.W. et al. Reaction $Pi$$Sup -$P $Yields$ N$Pi$$Sup +$$Pi$$Sup -$ at High Momentum Transfer., report, October 31, 1971; (https://digital.library.unt.edu/ark:/67531/metadc865579/m1/1/: accessed November 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .