a number of scholars have questioned the traditional model of proto-germanic "a"-mutation in whole or in part. in particular, the rare "a"-mutation of to "as a p[roto]-g[ermanic] phenomenon has always been contested." lloyd, for example, proposed an alternative explanation for all apparent instances of "a"-mutation of ; he suggested that "the partial overlapping in germanic of the two phonemes (represented in all environments by ) and (with the allophones and ) led to the occasional development of an "e"-allophone of "i" by systemic analogy". cercignani, on the other hand, argued that "no 'umlaut' phenomena can be assumed for proto-germanic", preferring to ascribe these changes to "the prehistory of the individual languages."