def cross(v1, v2):
    """
    Returns the cross product of the given two vectors
    using the formulaic definition

    """
    i = v1[1] * v2[2] - v2[1] * v1[2]
    j = v1[0] * v2[2] - v2[0] * v1[2]
    k = v1[0] * v2[1] - v2[0] * v1[1]
    return [i, -j, k]