@Override
    public boolean equals(Object o) {
      if (o == this) return true;
      if (!(o instanceof Pair)) return false;
      Pair that = (DependencyLinker.Pair) o;
      return left.equals(that.left) && right.equals(that.right);
    }
links are merged by mapping to parent/child and summing corresponding links
zipkin/src/main/java/zipkin2/internal/DependencyLinker.java