If the accented vowel is not in a constituent syllable synalepha may
occur.
Ex. _Mientras la cencia á descubrir no alcance_, p. 165, IV, l. 13.
(4) When the first word ends in a single vowel, and the second word
begins with a diphthong in a constituent syllable.
Ex. _Tú, proceloso austro que derribas_.
(3) and (4) might well be considered as cases of hiatus.