= Solution
Use an optional pair of <array indices>, so failure is distinct from every valid position:
``
def search(f: Array[Array[Int]], x: Int): Option[(Int, Int)]
``
\b[`Some((i,j))` denotes a match; `None` denotes absence.] The extra <array> argument makes the dependence on the searched data explicit; if `f` is already enclosed in the surrounding scope, it can instead be omitted. For all implementations below, assume `f` is non-null, its rows are non-null and rectangular, and it remains unchanged during the search. Empty dimensions are permitted.
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