Partially Flatten a Sequence


Write a function which flattens any nested combination of sequential things (lists, vectors, etc.), but maintains the lowest level sequential items. The result should be a sequence of sequences with only one level of nesting.
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(= (__ [["Do"] ["Nothing"]])
   [["Do"] ["Nothing"]])
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(= (__ [[[[:a :b]]] [[:c :d]] [:e :f]])
   [[:a :b] [:c :d] [:e :f]])
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(= (__ '((1 2)((3 4)((((5 6)))))))
   '((1 2)(3 4)(5 6)))

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