RobertJasiek: What about positions in that passing is best for both players? Is the miai value 0 then? If it is undefined for those positions, then I would like to define: The miai value is 0 then. Or should we rather leave miai value undefined then and refer to the temperature being 0 instead?
Bill: If correct, and not dictated by a ko or superko prohibition, a pass is worth 0 or less (down to -1 by territory scoring). See pass stones, AGA rules, and Spight rules for when a pass is worth -1.
The miai value of a gote is how much it gains, on average. If there is no penalty for an unconstrained pass, it simply leaves the board position unchanged. The value of the position is unchanged, and the gain is zero.