Write a propositional knowledge base describing the 4-Queen problem.

a. Solve the puzzle by deriving a model using DPLL using NO heuristics.

(Trace the steps, indicate what decisions are made in each iteration, indicate if and when back-tracking occurs, and indicate what the final solution is.)

b. "Solve" the puzzle by computing a model using DPLL using the PureSymbol and UnitClause heuristics.

(Trace the steps, indicate what decisions are made in each iteration, indicate if and when each heuristic is applied, and indicate what the final solution is.)

A B C D 4