  Recently, Blasiak-Morse-Seelinger introduced symmetric functions called
Katalan functions, and proved that the $K$-theoretic $k$-Schur functions due to
Lam-Schilling-Shimozono form a subfamily of the Katalan functions. They
conjectured that another subfamily of Katalan functions called the closed
$k$-Schur Katalan functions are identified with the Schubert structure sheaves
in the $K$-homology of the affine Grassmannian. The main result is a proof of
the conjecture.
  We also study a $K$-theoretic Peterson isomorphism that Ikeda, Iwao, and
Maeno constructed, in a non-geometric manner, based on the unipotent solution
of the relativistic Toda lattice of Ruijsenaars. We prove that the map sends a
Schubert class of the quantum $K$-theory ring of the flag variety to a closed
$K$-$k$-Schur Katalan function up to an explicit factor related to a
translation element with respect to an anti-dominant coroot. In fact, we prove
the above map coincides with a map whose existence was conjectured by Lam, Li,
Mihalcea, Shimozono, and proved by Kato, and more recently by Chow and Leung.
