has element at index `i` been set already? This is true after an explicit call to `put i v` for some value `v` or for indices in the range `0..length-1` for all indices that existed before `expand` was called.
0.095dev (2026-02-20 12:42:29 GIT hash dbcc3e4b3d2a59f66230b482cff8f0b018178d77 built by fridi@fzen)
call to `put i v` for some value `v` or for indices in the range `0..length-1`
for all indices that existed before `expand` was called.