Usually, in fuzzy logics, values from $[0,1]$ are considered. There are some three values logics for missing values such as Kleene's logic (http://www.filozof.uni.lodz.pl/bulletin/pdf/43_12_4.pdf).
My question is: how to combine them? That is how to build a logic that would have properties combining both logics on $[0,1]\cup\{u\}$ where $u$ is the Kleene's unknown. Specifically, I would like to know how to define the valuation the operators (And, Or, Neg). The problem is general, but for my purposes, fuzzy product logic is sufficient.
Any help or reference appreciated