  This note presents the classification of ladder operators corresponding to
the class of rational extensions of the harmonic oscillator. We show that it is
natural to endow the class of rational extensions and the corresponding
intertwining operators with the structure of a category REXT. The combinatorial
data for this interpretation is realized as a functor MD $\to$ REXT, where MD
refers to the set of Maya diagrams appropriately endowed with categorical
structure. Our formalism allows us to easily reproduce and extend earlier
results on ladder operators.
