Studying the book Understanding Morphology by Martin Haspelmath, I arrived at this fragment:
The importance of the latter part of the definition is seen in paradigms like insula. Although there are only seven different sequences of sounds in (2.3), we can still say that the paradigm of insula has ten word-forms, because ten different sets of grammatical functions are expressed (e.g. genitive singular and nominative plural are distinct, despite having the same form).
I thought a grammatical function was a relationship between constituents in a clause. So, my question is: why does the author gives genitive singular as an example? Is it supposed to be an inflection of the lexeme insula; a specific word-form?