code: private void addClause(final Collection<Literal> literals) {
          for (final Literal lit : literals) {
              Integer index = this.name2idx.get(lit.variable().name());
              if (index == null) {
                  index = this.name2idx.size() + 1;
                  this.name2idx.put(lit.variable().name(), index);
                  this.idx2name.put(index, lit.variable().name());
              }
              this.solver.addlit(lit.phase() ? index : -index);
          }
          this.solver.addlit(CLAUSE_TERMINATOR);
      }
docs: Adds a collection of literals to the solver.
  @param literals the literals