Do you use is or are in this conjunctive sentence?

Is.

"Device" is singular, and "set" is singular, therefore the noun is singular.

(The second noun is "set", not "devices" -- if the sentence read simply "If a set of devices is down . . .", then it may be easier to see that the verb there must agree with "set" and NOT with "devices".)

[ If the conjunction were "and", THEN the verb should be plural :

compare : "If A and B is down . . . "

with "If A and B are down . . . "

but, since you have "or",

"If A or B is down . . ." -- this requires the u se of "is".]

Ignoramus is correct because "or" is used. If it were "and" a plural verb would be used because then the subject would be plural: John or Sam is going. John and Sam are going.

All conjunctions of literals and all disjunctions of literals are in CNF, as they can be seen as conjunctions of one-literal clauses and conjunctions of a single clause, respectively. As in the disjunctive normal form (DNF), the only propositional connectives a formula in CNF can contain are and, or, and not. The not operator can only be used as part of a literal, which means that it can only precede a propositional variable.

BTW: CNF is conjunctions normal form

You would use "are" because its more than one thing that is 'down'

At least that makes sense, right? Iam only 16...

"are", because it follows the plural. I think?