Call to undefined function is_user_logged_in(), whats going on?

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Please look at the line 10,
if(is_admin() == false &&is_user_logged_in() == true){
it says: Call to undefined function is_user_logged_in()

I tried to restart the theme and the plugin, the error still in here.
if I stop the plugin it will no any problem.

But I can not understand. where is the error in this code?
Please help…