  The T-systems and Y-systems are classes of algebraic relations originally
associated with quantum affine algebras and Yangians. Recently the T-systems
were generalized to quantum affinizations of a wide class of quantum Kac-Moody
algebras by Hernandez. In this note we introduce the corresponding Y-systems
and establish a relation between T and Y-systems. We also introduce the T and
Y-systems associated with a class of cluster algebras, which include the former
T and Y-systems of simply laced type as special cases.
