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local M = {}

local complex_mt = {
    __tostring = function(self)
        if self.im == 0 then
            return tostring(self.re)
        elseif self.re == 0 then
            return (math.abs(self.im) == 1 and (self.im < 0 and "-" or "") or tostring(self.im)) .. "i"
        elseif self.im > 0 then
            return tostring(self.re) .. "+" .. (math.abs(self.im) == 1 and "" or tostring(self.im)) .. "i"
        elseif self.im == 1 then
            return tostring(self.re) .. "+i"
        elseif self.im == -1 then
            return tostring(self.re) .. "-i"
        else
            return tostring(self.re) .. tostring(self.im) .. "i"
        end
    end,
    __add = function(z1, z2)
        if type(z2) == "number" then z2 = M.complex(z2) end
        return M.complex(z1.re + z2.re, z1.im + z2.im)
    end,
    __sub = function(z1, z2)
        if type(z2) == "number" then z2 = M.complex(z2) end
        return M.complex(z1.re - z2.re, z1.im - z2.im)
    end,
    __mul = function(z1, z2)
        if type(z2) == "number" then z2 = M.complex(z2) end
        return M.complex(z1.re * z2.re - z1.im * z2.im,
                         z1.re * z2.im + z1.im * z2.re)
    end,
}

-- makes a new complex number.
M.complex = function(re, im)
    local res = {re = re or 0, im = im or 0, type = "complex"}
    setmetatable(res, complex_mt)
    return res
end

M.sqrt = function(n)
    if type(n) == "number" and n < 0 then
        return M.complex(0, math.sqrt(-n))
    else
        return math.sqrt(n)
    end
end

M.i = M.complex(0, 1)

return M