Assertion: diphthong's vowel | /r/HasProperty | the same
Facets:
value: always
type: DEGREE
value: as in boot
type: OTHER
Source sentences:
text: If two vowels in a row are the same, as in boot or beer, then it's not a diphthong.
text: The vowels which form triphthongs are always the same: closed + open + closed – or what is the same: