001: 1015
003: Starlibrary PMS 4.5
005: 20180430
020: ^a81-224-0090-6
066: ^ale.d
072: ^aalgebraic systems
082: ^a004.9
100: ^aleon. S> Levy
240: ^adiscrete structures of computer science
245: ^adiscrete structures of computer science
260: ^c1993
650: ^adirected graphs
650: ^asets
650: ^afunctions
650: ^aand relations