-## Comprehensions
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-3. Using either Kapulet's or Haskell's list comprehension syntax, write an expression that transforms `[3, 1, 0, 2]` into `[3, 3, 3, 1, 2, 2]`.
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-*Here is a hint*
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-Define a function `dup (n, x)` that creates a list of *n* copies of `x`. Then use list comprehensions to transform `[3, 1, 0, 2]` into `[[3, 3, 3], [1], [], [2, 2]]`. Then use `join` to "flatten" the result.
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## Lists
7. Continuing to encode lists in terms of their left-folds, how should we write `head`? This is challenging.