AIP Conference Proceedings [AIP Publishing PROCEEDINGS OF THE SECOND INTERNATIONAL CONFERENCE ON FRONTIERS IN INDUSTRIAL AND APPLIED MATHEMATICS (FIAM-2019) - Noida, India (21–22 December 2019)] PROCEEDINGS OF THE SECOND INTERNATIONAL CONFERENCE ON FRONTIERS IN INDUSTRIAL AND APPLIED MATHEMATICS (FIAM-2019) - On an M/G/1 queue providing general first essential service with customer’s choice for general or deterministic second optional service