def find_component_to_lower(fun):
    """Determine which exponent/component of a basis function to lower.

    The first component with a non-zero value will be the result.

    Arguments:
    fun -- The coefficients for a single basis function (list of 3 integers).
    """

    for i, c in enumerate(fun):
        if c > 0:
            return i

    return -1