known to have odd parity (-1): unless the relative motion of the products was unusual, decay into three pions predicted odd "τ" kaon parity [1=(-1)³ = -1], but decay into two pions predicted even "θ" kaon parity [1=(-1)² = 1].

As more data was accumulated on the properties of the decay products, it became clear that every property of these particles was identical except for their parity. It seemed possible that these were the same particle except for this violation of parity. This was known as the {{math.