What a funny letter, it looks so cute

[Cifi]

I found this one today in "Η πρώτη ημέρα του Μαΐου".
ΐ
While I knew the two dots as in indication to separately pronounce a vowel (e.g. in Spanish "pingüino") and the accent mark on stressed syllables, I have never seen them combined before. Isn't it lovely?

[LICA98]

you should try Vietnamese then, they have loads of letters with combined diacritics

[sotos_greece]

UPDATE (30+ years now)
Due to the new "monotonic system" of writing which is now the current system in Greece
(prior to the "polytonic" which some use a lot and is not foul to use it)
When a words that intonates and must have those "two upper dots" (διαλυτικά), then those "two upper dots" (διαλυτικά) are omitted.
for e.g. "Μαίου" is the correct. not the "Μαΐου"
But in word "Υϊός" (=the son) the intonation is on "ό" so the "two upper dots" (διαλυτικά) stay in place on the " ϊ "
another example is ofc "κορονοϊός" (corona-virus) (...away from us...)

[LICA98]

UPDATE (30+ years now)
Due to the new "monotonic system" of writing which is now the current system in Greece
(prior to the "polytonic" which some use a lot and is not foul to use it)
When a words that intonates and must have those "two upper dots" (διαλυτικά), then those "two upper dots" (διαλυτικά) are omitted.
for e.g. "Μαίου" is the correct. not the "Μαΐου"
But in word "Υϊός" (=the son) the intonation is on "ό" so the "two upper dots" (διαλυτικά) stay in place on the " ϊ "
another example is ofc "κορονοϊός" (corona-virus) (...away from us...)

so what is this then?
https://el.wikipedia.org/wiki/1_Μαΐου

[O.Zoe]

UPDATE (30+ years now)
Due to the new "monotonic system" of writing which is now the current system in Greece
(prior to the "polytonic" which some use a lot and is not foul to use it)
When a words that intonates and must have those "two upper dots" (διαλυτικά), then those "two upper dots" (διαλυτικά) are omitted.
for e.g. "Μαίου" is the correct. not the "Μαΐου"

They are omitted only when the accent is on α. For example, γάιδαρος (donkey). In this case, there's no need to include them because the accent mark on α indicates that we don't have the digraph αι (/e/). So, Μάιος doesn't take διαλυτικά (diaeresis) in nominative case, but in genitive case they are mandatory (Μαΐου = /ma'i.u/), otherwise we would pronounce it /'me.u/ (Μαίου). : )

See the following two sentences.
Θέλω να φάω παιδάκια. vs. Θέλω να φάω παϊδάκια.

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But in word "Υϊός" (=the son) the intonation is on "ό" so the "two upper dots" (διαλυτικά) stay in place on the " ϊ "
another example is ofc "κορονοϊός" (corona-virus) (...away from us...)

"Υϊός" is not correct, because υι is a digraph, pronounced as one phoneme. It's υιός (/iˈos/ = son). On the other hand, κορονοϊός takes the diaeresis because we don't have the digraph οι. It's a compound noun from the words κορόνα (corona) and ιός (virus).

[sotos_greece]

[
p.s. "Υϊός" IS correct on ALL polytonic and ALL religional and ancient texts.
Ofc, grammar has disputes over time ... that's it how it evolves.
Btw.. 40 years of Monotonic system can NOT erase 3000 years of polytonics . Let's not open this Aeolus sack of winds eh ?

]