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in coelo --> in coelis/ in caelis

'Havens' more often are expressed in the plural form "caeli".

Do you remember: "Pater noster, qui es in caelis..." etc?

I didn't know.

[/note]Moreover, in Italian we say "Padre nostro, che sei nei cieli" [/note]

Yes, I believe that we definitely can see an influence of Latin here which is not unusual for Italian language at all.