Neutrons are fermions and so obey Fermi–Dirac statistics, which implies that the final state is antisymmetric. Using the fact that the deuteron has spin one and the pion spin zero together with the antisymmetry of the final state they concluded that the two neutrons must have orbital angular momentum L = 1 . The total parity is the product of the intrinsic parities of the particles and the extrinsic parity of the spherical harmonic function ( − − 1 ) L . Since the orbital momentum changes from zero to one in this process, if the process is to conserve the total parity then the products of the intrinsic parities of the initial and final particles must have opposite sign. A deuteron nucleus is made from a proton and a neutron, and so using the aforementioned convention that protons and neutrons have intrinsic parities equal to + 1 they argued that the parity of the pion is equal to minus the product of the parities of the two neutrons divided by that of the proton and neutron in the deuteron, explicitly ( − − 1 ) ( 1 ) 2 ( 1 ) 2 = − − 1 , from which they concluded that the pion is a pseudoscalar particle.