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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def table_is_subset_of(entries_a, entries_b):
 """Check that every key matched by every entry in one table results in the same route when checked against the other table. For example, the table:: is a functional subset of a minimised version of itself:: False True But not vice-versa:: False Default routes are taken into account, such that the table:: is a subset of the empty table:: True Parameters Ordered of lists of routing table entries to compare. Returns ------- bool True if every key matched in `entries_a` would result in an equivalent route for the packet when matched in `entries_b`. """

    # Determine which bits we don't need to explicitly test for
    common_xs = get_common_xs(entries_b)

    # For every entry in the first table
    for entry in expand_entries(entries_a, ignore_xs=common_xs):
        # Look at every entry in the second table
        for other_entry in entries_b:
            # If the first entry matches the second
            if other_entry.mask & entry.key == other_entry.key:
                if other_entry.route == entry.route:
                    # If the route is the same then we move on to the next
                    # entry in the first table.
                    break
                else:
                    # Otherwise we return false as the tables are different
                    return False
        else:
            # If we didn't break out of the loop then the entry from the first
            # table never matched an entry in the second table. If the entry
            # from the first table could not be default routed we return False
            # as the tables cannot be equivalent.
            default_routed = False

            if len(entry.route) == 1 and len(entry.sources) == 1:
                source = next(iter(entry.sources))
                sink = next(iter(entry.route))

                if (source is not None and
                        sink.is_link and
                        source is sink.opposite):
                    default_routed = True

            if not default_routed:
                return False

    return True