Pyuvor je Gravor

Ceqli grammar words (pyuvor) are in the shape CV, that is, one cwazim followed by one vawl.  See HERE.  Now, Ceqli regards the difference between Pyuvor and Gravor (content words) to be fuzzy, in keeping with the Gödel theory of linguistics.  So sometimes it's hard to decide which a given word should be.  Currently, Ceqli has ko and de, for to and from.

Go don hon ko zi.  I give a book to you.
Go pren hon de zi.  I take a book from you.

Now, other prepositions are gravor:

Go ziq ben zi.  I sing benefit you, or I sing for you.

Go dan cwaq dorm.  I in the bed sleep.

So why should to and from be any different?  Is it because they seem so much like case endings in my mind?  Or is it because, as lone verb/prepositions, they're hard to translate?  Or are they?

Go ko do.  I to the house.  Maybe it means I'm on my way to the house.
Go de Doycehaym.  I'm from Germany.

So, they don't seem to be any different from ben or dan or sur.  I propose, then, to replace ko/de with tsu/del.  Please give me feedback.