@article {Vel86a,
AUTHOR = {Veli{\v{c}}kovi{\'c}, Boban},
TITLE = {Playful {B}oolean algebras},
JOURNAL = {Trans. Amer. Math. Soc.},
FJOURNAL = {Transactions of the American Mathematical Society},
VOLUME = {296},
YEAR = {1986},
NUMBER = {2},
PAGES = {727--740},
}