original.name="For_Valid_6"
======
>>> main.whiley
type nat is (int x) where x >= 0
function sum(nat[] items) -> nat:
int r = 0
for i in 0..|items| where r >= 0:
r = r + items[i]
// Done
return (nat) r
public export method test():
assume sum([1]) == 1
assume sum([1,2]) == 3
assume sum([1,2,3]) == 6
assume sum([1,2,3,4,5,6]) == 21
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