A study is made of conditions on a language L which ensure that the smallest intersection-closed full AFL containing L (written @@@@ @@@@(L)) does or does not contain all recursively enumerableâ€¦ (More)

The purpose of this paper is to show that a number of well-known families have property (*). In particular, we prove that the family of context-free languages does indeed have this property. Inâ€¦ (More)

The amount of nondeterminism that a pushdown automaton requires to recognize an input string can be measured by the minimum number of guesses that it must make to accept the string, where guesses areâ€¦ (More)

Two transformations are presented which, for any pushdown automaton (PDA)M withn states andp stack symbols, reduce the number of stack symbols to any desired numberpâ€² greater than one. The firstâ€¦ (More)