local function linear_combo(c)
    local sb = ""
    local i = 0
    for c as n do
        if n != 0 then
            local op = (n < 0 and sb == "") ? "-"   :
                       (n < 0)              ? " - " :
                       (n > 0 and sb == "") ? ""    : " + "
            local av = math.abs(n)
            local coeff = (av == 1) ? "" : $"{av}*"
            sb ..= $"{op}{coeff}e({i + 1})"
        end
        ++i
    end
    return (sb == "") ? "0" : sb
end

local combos = {
    {1, 2, 3},
    {0, 1, 2, 3},
    {1, 0, 3, 4},
    {1, 2, 0},
    {0, 0, 0},
    {0},
    {1, 1, 1},
    {-1, -1, -1},
    {-1, -2, 0, -3},
    {-1}
}
for combos as c do
    print(string.format("%-13s  ->  %s", c:concat(", "), linear_combo(c)))
end