Nested comprehension with filter

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Accepted Answer

An if clause at the end of a comprehension filters which elements make it into the result. The nested for loops flatten the matrix in row-major order, giving 1 through 9, and then only the even values (2, 4, 6, 8) pass the filter. The order of clauses matters: for ... for ... if is 'outer loop, inner loop, filter' - the filter applies per inner element.