code: protected void assume(final int decision) {
          assert propagated();
          this.level++;
          final int height = this.trail.size();
          this.control.push(new CLFrame(decision, this.level, height));
          assert this.level + 1 == this.control.size();
          assign(decision, null);
      }
docs: Assumes a given decision.
  @param decision the decision