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(a|b)*b(a|b)*No lookaheads — restructure insteadvs Programming RegexFormal RE✨ Emoji Combos

Programming regex can use (?=.*b) lookahead. Formal RE must express "contains b" by restructuring: (a|b)*b(a|b)*. No zero-width assertions.

✓ Accepts
babbaabbbabaab
✗ Rejects
εaaaaaa
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