I've been developing an android app. I'm a long-time android user and from my experience, I rarely (if never) use the up button provided at the top left of the activity and always use the back button and the bottom of the screen (either physical or on-screen).
I'm wondering if this is the case for most users? Is the back button sufficient or should I always provide an up button (iOS style) at the top left of the screen? Keep in mind that, in my app, the back and up buttons do essentially the same thing.