A simple universal current-current theory of weak interactions now accounts fairly well for all weak phenomena except the nonleptonic | Δ I _ |   =   1 / 2 https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780429496615/7c8aa2fe-acca-4ba8-aa16-0305d19eb299/content/eq1536.tif"/> rule, which presumably should be generalized to a unitary octet rule, covering not only the familiar |ΔY| = 1 nonleptonic interactions but also the |ΔY| = 0 nonleptonic interactions (for which experimental evidence in heavy nuclei has been presented by Boehm and Kankeleit).

One may account for the octet nonleptonic rule either (a) by a theory that adds extra current-current products for strongly interacting particles alone, or else (b) by a dynamical mechanism that enhances octets by means of strong interactions. It is interesting that we can distinguish any reasonable theory of type (a) from any theory of type (b) by the amount of | Δ I _ |   =   1 https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780429496615/7c8aa2fe-acca-4ba8-aa16-0305d19eb299/content/eq1537.tif"/> in the ΔY = 0 nonleptonic interaction; the | Δ I _ |   =   1 https://s3-euw1-ap-pe-df-pch-content-public-u.s3.eu-west-1.amazonaws.com/9780429496615/7c8aa2fe-acca-4ba8-aa16-0305d19eb299/content/eq1538.tif"/> component is large in the former case and small in the latter case. Difficult experiments involving light nuclei may be able to resolve the two possibilities.