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472
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def urbanmain() = {
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  import M3._
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221
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472
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  assert(nullable(ZERO) == false)
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  assert(nullable(ONE) == true)
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  assert(nullable(CHAR('a')) == false)
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  assert(nullable(ZERO | ONE) == true)
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  assert(nullable(ZERO | CHAR('a')) == false)
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  assert(nullable(ONE ~  ONE) == true)
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  assert(nullable(ONE ~ CHAR('a')) == false)
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  assert(nullable(STAR(ZERO)) == true)
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  assert(nullable(ALTs(List(ONE, CHAR('a'), ZERO))) == true)
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  assert(nullable(SEQs(List(ONE, ALTs(List(ONE, CHAR('a'), ZERO)), STAR(ZERO)))) == true)
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}
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