Massimo Caliman
by Massimo Caliman
~1 min read


  • Programming


  • Finite Automata
  • Finite-State Machine

Kleeneliness is next to Gödeliness

A language L 1 not can be deterministically recognised by empty stack 2 if there exist two distinct strings of L such that one is prefixed by the other.

In more formal terms if ∃ u,v ∈ L : u is prefixed by v where the concept, of prefix can be further formalised as v = ux where x is a string of the alphabet to which both strings u and v belong.

The usefulness of this property is obvious as it allows us to realise that if we are wasting time trying to develop an elementary parser using a PDA for a given language that contains strings of the type aabb and aabbbb, the automaton will stop, by empty stack, as soon as the prefix is consumed.

  1. This will be demonstrated in a future post. 

  2. So from a Pushdown Automata (PDA)