Joxan Jaffar
Journal of the ACM
Lengauer and Tarjan proved that the number of black and white pebbles needed to pebble the root of a tree is at least half the number of black pebbles needed to pebble the root. This result is extended to a larger class of acyclic directed graphs including pyramid graphs. © 1985, ACM. All rights reserved.
Joxan Jaffar
Journal of the ACM
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