original.name="ConstrainedList_Valid_17"
======
>>> main.whiley
type nat is (int x) where x >= 0
function f(nat[][] xs) -> nat[]
requires |xs| > 0:
return xs[0]
public export method test() :
nat[] rs = f([[1, 2, 3], [4, 5, 6]])
assume rs == [1,2,3]
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