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(a|b)*aa(a|b)*(a|b)*aa(a|b)* — contains substring "aa"CombinedFormal RE✨ Emoji Combos

Full-string match + surrounding (a|b)* simulates substring search within formal RE. The inner "aa" must appear somewhere in the string.

✓ Accepts
aaaabbaabaabaaaa
✗ Rejects
εababbababa
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