@article {Vel91,
AUTHOR = {Veli{\v{c}}kovi{\'c}, Boban},
TITLE = {C{CC} posets of perfect trees},
JOURNAL = {Compositio Math.},
FJOURNAL = {Compositio Mathematica},
VOLUME = {79},
YEAR = {1991},
NUMBER = {3},
PAGES = {279--294},
}