Refactor AbstractProver flags

src/org/sosy_lab/java_smt/api/BasicProverEnvironment.java

@@ -145,7 +145,7 @@ default ImmutableList<Model.ValueAssignment> getModelAssignments() throws Solver
    * combined.
    *
    * @param assumptions Selected assumptions.
-   * @return Empty optional if the constraints with assumptions are satisfiable, subset of
+   * @return {@link Optional#empty()} if the constraints with assumptions are satisfiable, subset of
    *     assumptions which is unsatisfiable with the original constraints otherwise.
    */
   Optional<List<BooleanFormula>> unsatCoreOverAssumptions(Collection<BooleanFormula> assumptions)

src/org/sosy_lab/java_smt/basicimpl/AbstractEvaluator.java

@@ -37,6 +37,10 @@ protected AbstractEvaluator(
     this.creator = Preconditions.checkNotNull(creator);
   }
 
+  protected final boolean isProverClosed() {
+    return prover.isClosed();
+  }
+
   @SuppressWarnings("unchecked")
   @Nullable
   @Override
@@ -128,7 +132,12 @@ protected final Object evaluateImpl(TFormulaInfo f) {
     return evaluatedF == null ? null : creator.convertValue(f, evaluatedF);
   }
 
-  protected boolean isClosed() {
+  /**
+   * Returns the closed status of the evaluator (and only the evaluator!).
+   *
+   * @return {@code true} if it is closed, {@code false} else.
+   */
+  protected final boolean isClosed() {
     return closed;
   }