There is currently no problem, but we will support SplitPoint.BEGIN in the future, it may be necessary to check whether it has already been marked (if it has been marked, report an error?). For example, split_spec is written as follows: split_spec={"layer.0" : SplitPoint.END, "layer.1" : SplitPoint.BEGIN}, in first loop, layer.0 will be marked on layer.1, and then in second loop, it will be marked again by layer.1

According to the current logic, there will be no problem with repeated markings, because the marking method is to assign a value of 1.