2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/64843Boardman, Johnson, and Wilson gave a precise formulation for an unstable algebra over a generalized cohomology theory. Modifying their definition slightly in the case of complex K-theory by taking into account its periodicity, we prove that an unstable algebra for complex $K$-theory is precisely a filtered $λ$-ring, and vice versa.17 pagesAlgebraic Topology55N20,55N15,55S05,55S25text