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Tape‑n‑Trace
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PDA Simulator

Hopcroft 2e §6.1–6.2. A PDA is a finite automaton plus a stack, and its whole truth at any moment is the instantaneous description (q, w, γ). This page runs the ID relation ⊢ in front of you: three synced panels, the branch tree for every guess, and the ID sequence in the notation your answer sheet wants.

Build your own in the PDA editor, or watch final state ↔ empty stack and grammar → PDA.

Machines
Try
a, Z0/AZ0, a, A/AAb, A/εb, A/εε, Z0/Z0ε, Z0/Z0q0q1q2

Narration

Enter a string and press Run to step through the machine.

aⁿbⁿ — the matched countHopcroft 2e §6.1.4

Push an A for every a, pop one for every b; the stack is the counter no finite automaton has.

Accepts by final state · nondeterministic — 1 overlapping move pair; see the editor for the pair-by-pair report.