from typing import OrderedDict


def merge_list(col1, col2):
    """
    Given two sequences col1 and col2, returns a list of the
    items in them, in order, omitting any from col2 that are also
    in col1.
    """
    cs = OrderedDict()
    for c in col1:
        cs[c] = 0.0
    for c in col2:
        cs[c] = 0.0
    return list(cs.keys())