[tremon]

It wouldn't be. The goal is to separate the second o from the first, not to separate the o from the c:

The diaeresis indicates that a vowel should be pronounced apart from the letter that precedes it [1]

[1] https://en.wikipedia.org/wiki/Diaeresis_%28diacritic%29#Diae...

[eru]

Oh, true. Naive should have tipped me off.