Grötschel, L. Lovász, A. Schrijver: Geometric Algorithms and Combinatorial Optimization, Springer, 1988
Around 1980, Korte and Lovász introduced the greedoid to further generalize this characterization of greedy algorithms; hence the name greedoid.
Lovász, M.D. Plummer: Matching Theory, Akadémiai Kiadó - North Holland, Budapest, 1986