x = {
    a = 10,
    b = 20,
    c = 30
}

print(x.a);
print(x.b);
print(x.c);

y = {
    d = 40,
    e = 50,
    f = 60
}

z = {
    g = 70,
    h = 80,
    i = 90
}

setmetatable(z, {
    __index = function(object, key)
        if x[key] then return x[key] end
        if y[key] then return y[key] end
        return nil
    end
})

print(z.a); -- 10
print(z.d); -- 40
print(z.g); -- 70

-- this is pretty unoptimized
-- and it uses meta-programming
-- which I don't require
-- this may have errors
-- but the gist is clear