<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def cli(env, identifier):
 """Cancel a subnet."""


    mgr = SoftLayer.NetworkManager(env.client)
    subnet_id = helpers.resolve_id(mgr.resolve_subnet_ids, identifier,
                                   name='subnet')

    if not (env.skip_confirmations or formatting.no_going_back(subnet_id)):
        raise exceptions.CLIAbort('Aborted')

    mgr.cancel_subnet(subnet_id)