def default_wire_map(ops):
    """Create a dictionary mapping used wire labels to non-negative integers

    Args:
        ops Iterable[Operation]

    Returns:
        dict: map from wires to sequential positive integers
    """

    # Use dictionary to preserve ordering, sets break order
    used_wires = {wire: None for op in ops for wire in op.wires}
    return {wire: ind for ind, wire in enumerate(used_wires)}