<Li> On the death of the first Prime Minister, Lee Kuan Yew, who died on 23 March 2015 . </Li> <Li> On the death of 7 pupils, 1 teacher and a guide from Tanjong Katong Primary School due to 2015 Sabah earthquake . </Li> <Li> On the death of the sixth President of Singapore, S.R. Nathan, who died on 22 August 2016 . </Li> <Li> On the death of a former Cabinet Minister, Othman Wok, who died on 17 April 2017 . </Li>

What is the protocol for flags at half mast