reduce Examples
lreduce(+, 0, [6, 7, 8, 9]) ==> 30

lreduce(*, 1, [6, 7, 8, 9]) ==> 3024

lreduce(append, [ ], [[1, 2, 3], [4, 5], [6]])
     ==> [1, 2, 3, 4, 5, 6]
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