caleb531 / automata / 27617777170

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Fix {0} quantifier accepting one occurrence (#289)

The {0} (i.e. {0,0}) quantifier built an NFA that accepted both the empty
string and a single occurrence of the sub-pattern, so a{0} matched "a".
Python's re and standard regex semantics make X{0} match the empty string
only.

In repeat(), the pattern's final states were added whenever
lower_bound <= 1, including the degenerate upper_bound == 0 case. Exclude
that case so {0,0} contributes only the empty path; {0,}, {0,n} and all
other bounds are unaffected.

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