function connect(target, sources) {
    const targetRank = target.rank,
      n = sources.length;
    for (let i = 0; i < n; ++i) {
      if (targetRank < sources[i].rank) {
        this.rerank(target);
        return;
      }
    }
  }
Connect a target operator as a dependent of source operators.
If necessary, this method will rerank the target operator and its
dependents to ensure propagation proceeds in a topologically sorted order.
@param {Operator} target - The target operator.
@param {Array<Operator>} - The source operators that should propagate
  to the target operator.