Proto-Indo-European *p was lost in Proto-Celtic, apparently going through the stages *ɸ (as in the table above) and *h (perhaps attested by the toponym Hercynia if this is of Celtic origin) before being lost completely word-initially and between vowels.
O *p protoindoeuropeo perdeuse no protocelta, aparentemente atravesando os estadios *φ (como na táboa superior) e *h (talvez confirmado pelo topónimo Hercynia, se este for de orixe céltica) antes de desaparecer completamente no inicio das palabras e entre vogais.