2DPDA

Two-way deterministic pushdown automata aka 2-iterated pushdown automata

See:

• Two-way pushdown automata
  • $\{a^nb^nc^n \mid n \geq 1\}$
  • $\{a^{2^n} \mid n \geq 1\}$
• Simulation of Two-Way Pushdown Automata Revisited