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a|εOptionality via ε: a|εAlternationFormal RE✨ Emoji Combos

The formal way to express "a is optional". Programming regex writes a?; formal RE writes (a|ε). This is the theoretical definition of the ? quantifier.

✓ Accepts

εa

✗ Rejects

baaab

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Regular Expression Pattern

Flavor

/

/

Test String

Annotation

Unable to parse pattern

Active Flags:

gglobal: Don't return after first match

mmultiline: ^ and $ match start/end of each line

Match Results

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