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(a|b)*a(a|b)(a|b)(a|b)*a(a|b)(a|b) — 3rd from end is aClassic ProblemsFormal RE✨ Emoji Combos

Classic NFA exercise: guess nondeterministically when you're 3 from the end. The minimal DFA has 8 states (subset construction on 4-state NFA).

✓ Accepts
aaaaababaabbbaabbabb
✗ Rejects
εaabbbabbb
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