We all love sparsity: it makes computations faster, guarantees tighter, and interpretations easier. In our paper, , which will appear in TMLR, we introduce a new type of sparsity, which we term “cardinality sparsity”. We show that cardinality sparsity has all the usual perks, and more importantly, we demonstrate that it is also a very powerful concept for matrix-matrix multiplications. Indeed, cardinality sparsity can speed up such computations and reduce memory usage dramatically. Well done, Ali! 👍👍👍