Condition, Karaoke

I taught my student necessary and sufficient condition. It's not easy for most of people. At first I didn't understand well. I think one of the reason is the way texts shows us is not good. But it is not all of reasons. Logic is difficult.
I ate Thai dishes with my friends at night. Good meals made me happy. Then we went to sing to Sidax. There were a lot of people, because they finished work in this year and had time to play, sing. I wonder these scenes were seen in only Japan.