where the sum and maximum are taken over literals involving variables in .

**Proof.** Suppose that all of the variables in are unvalued or
satisfied. Now let be any unvalued literal in . If
, then
and thus
since
. If, on the other hand, , then

and

Combining these, we get

Either way, we cannot have and Proposition 3.8 therefore implies that cannot be unit. It follows that is a watching set.

The converse is simpler. If , value every literal outside of so as to make false. Now , so if is the literal in with greatest weight, the associated weight satisfies and is unit. Thus cannot be a watching set.

This generalizes the definition from the Boolean case, a fact made even more obvious by:

**Proof.** The expression (22) becomes

or