I learnt that superlatives have a partitive singular in -tA, so for instance lähin, lähintä, but then my book has sentences where the partitive is in -impAA:
And the Wiktionary template for Finnish superlatives gives the endings -impAA and -impAtA as alternatives for the partitive singular, as well as -innA for the essive singular, but these forms don’t show up on the individual words’ pages, and they are not listed by KOTUS (type 36) either.Leena tulee lähelta.
Kalle tulee vielä lähempää.
Eila tulee kaikkein lähimpää.
So I’d like to know if these forms are common alternatives, or if they are used only for some words, or in some constructions.