import mir.ndslice;
auto a = [1, 2, 3, 9].sliced.series(iota!int([4], 1));
auto b = [0, 2, 4, 9].sliced.series(iota!int([4], 1) * 10.0);
alias unionAlgorithm = troykaSeries!(
    (key, left) => left,
    (key, left, right) => left + right,
    (key, right) => -right,
);
auto c = unionAlgorithm(a, b);
assert(c.index == [0, 1, 2, 3, 4, 9]);
assert(c.data == [-10, 1, 22, 3, -30, 44]);