import math


def halve(l):
    """
    Split a sequence in half, biased to the left (if the number of elements
    is odd, the left sub-list has one more element than the right sub-list.)

    :param list l: The sequence to split
    :return: a `tuple` containing both halves of the sequence.
    """
    half_index = int(math.ceil(len(l) / 2.0))
    return (l[:half_index], l[half_index:])