in the task of brain tumor segmentation of the brats challenge, they say : "The participants are called to address this task by using the provided clinically-acquired training data to develop their method and produce segmentation labels of the different glioma sub-regions. The sub-regions considered for evaluation are the "enhancing tumor" (ET), the "tumor core" (TC), and the "whole tumor" (WT) ", my problem with this statement is that when training a segmentation model, each pixel is expected to belong to one and only class, but in this case a pixel is granted to belong always to the "whole tumor" class and also to either the "enhancing core" or "enlacing tumor" class, wouldn't this confuse the model as pixel need to be classified as two classes?