The scenario
Build the ε-NFA for the unsigned integer regex [0-9]+ using Thompson construction, showing the plus operator's epsilon back-edge.
What is in this drawing
Read the decisions behind it.
01
Introduce an ε-transition from the digit acceptor back to its start to model one-or-more repetition.
02
Use a final state reached by ε after the digit to preserve acceptance of exactly one digit.
03
Label the digit transition with the character class [0-9] rather than each individual digit.
Reusable whenever converting any `+` regex operator into an NFA; swap the base subexpression's NFA and reuse the same ε wiring.
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