def disc(f):
    """
    Return the discriminant of the given quadratic form 'f'.
    f = [a, b, c]
    """
    if len(f) != 3:
        raise TypeError("form must be composed of 3 integers")
    for i in f:
        if not isinstance(i, int):
            raise TypeError("all components must be integers")
    return (f[1]*f[1] - 4*f[0]*f[2])