Approximately 10% of the training tasks (and no test tasks) represent protein complexes (i.e. more than one protein). For these tasks, we calculated the distance of the target protein with all the proteins in the complex and selected the largest distance. The result of the calculation of the distances between the proteins in the test and training tasks is an N_train*N_test matrix ( ). EXT_PROT is determined for each task based on 𝐷 𝑁 𝑡𝑟𝑎𝑖𝑛 * 𝑁 𝑡𝑒𝑠𝑡 this matrix. The output is a N_test dimensional vector in which each element indicates the EXT_PROT of a particular task. For this purpose, we utilize the average of k-nearest source tasks to assign a hardness value to each test task. Additional information on determining protein representations for all source and target tasks is provided in the Supporting information.