EXT_CHEM, EXT_PROT and INT_CHEM. The two external components define the hardness of a target task based on the source tasks (i.e., the distance between the source tasks and the test task). The chemical space hardness is defined by the distance between the chemical space of the small molecules of the source tasks and the target task (Figure ). Likewise, the protein space hardness is defined by the distance between the representations of the proteins of the source tasks and the target task (Figure ). The internal component is solely a function of the target task and does not access any information related to the source tasks. It measures the inherent difficulty of the task based on machine learning performance on the internal train and test split without considering external information.