 Each phase involves one single change which applies equally to the labials () and their equivalent dentals (), velars () and rounded velars ().The first phase left the phoneme repertoire of the language without voiceless stops, the second phase filled this gap, but created a new one, and so on until the chain had run its course.When two obstruents occurred in a pair, the first was changed according to Grimm's law, if possible, while the second was not.