  The plethystic Murnaghan-Nakayama rule describes how to decompose the product
of a Schur function and a plethysm of the form $p_r\circ h_m$ as a sum of Schur
functions. We provide a short, entirely combinatorial proof of this rule using
the labelled abaci introduced in Nicholas A. Loehr. Abacus proofs of Schur
function identities. In: SIAM J. Discrete Math. 24.4 (2010), pp. 1356-1370.
