The sum and substance of the above proviso is that a candidate who has already been allocated to the IPS/Central Services Group 'A ' and who in order to improve his efficacy of selection to higher civil service, expresses his inten tion to appear in the next CSE (Main) for competing for IAS, IFS, IPS or Central Services Group 'A ' and who has been permitted to abstain from the Probationary Training in order to do so, will become eligible to appear in the next CSE (Main) but subject to the provisions of Rule 17, and that the said candidate when allocated to a service on the basis of the next Civil Services (Main) Examination can either join that service or the service to which he has already been allocated on the basis of the previous CSE and that if he fails to join either of the services, his allocation based on one or both the examinations, as the case may be, will stand cancelled.