If there is a tréma above the second vowel, both vowels are pronounced separately: aë , aü , eü and oë . However, disyllabic eu in morpheme borders is traditionally written without the tréma: 'my'.
if there is a tréma above the second vowel both vowels are pronounced separately aë  aü  eü and oë  however disyllabic eu in morpheme borders is traditionally written without the tréma 'my'