Question: n epsi - free PDA is a PDA with two modifications: that does not have any epsi transitions ( having epsi for
n epsi free PDA is a PDA with two modifications:
that does not have any epsi transitions having epsi for stack actions is OK and
it can push multiple symbols in one transition however it can pop at most one symbol per transition
That isQSigma Gamma delta q F is an epsi free PDA iff it is a PDA with the following modified transition function:
delta : Q times Sigma times Gamma epsi P Q times Gamma
Here, P A is the powerset of A that contains only finite sets. Note that there are differences to delta :
The second argument of delta cannot be epsi
q in Qsigma in Sigma gamma in Gamma epsi delta qsigma gamma returns a finite set of pairs made up of a state, and a sequence of symbols
from the stack alphabet as opposed to a state and a single stack symbol or epsi from the definition of a normal
PDA
The accepting criterion for epsi free PDA follow the same form presented for PDA in the lectures.
Prove or disprove: the class of languages epsi free PDA recognize is the class of contextfree languages.
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