Abstract
For an integers letl s (n), thes-iterated logarithm function, be defined inductively:l 0 (n)=n,l s+1 (n)=log2 (l 2 (n)) fors≧0. We show that for every fixeds and alln large enough, there is ann-vertex 3-pushdown graph whose smallest separator contains at leastΩ(n/l s (n)) vertices.
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The work of the first author was supported in part by NSF Grants MCS-83-03139, DCR-85-11713 and CCR-86-05353.
The work of the second author was supported in part by NSF Grants MCS-84-16190.