(diff ([1, 2, 3, 4]) == [1, 1, 1]
 && diff ([1, 3, 7, 19], 2) == [2, 8]
 && diff ([1, 2; 5, 4; 8, 7; 9, 6; 3, 1]) == [4, 2; 3, 3; 1, -1; -6, -5]
 && diff ([1, 2; 5, 4; 8, 7; 9, 6; 3, 1], 3) == [-1, -5; -5, 0]
 && isempty (diff (1)))
