1. the user uses the fingers of one hand only to make gestures. We
assume that the smart device is held in the other hand of the
user. Of course, the user can lay the device down on a table and
use both hands, but in consideration of common circumstances,
all gestures are assumed to be made with one hand;
2. the system does not require detailed/accurate input from the
user (e.g., selecting a point of an edge) because it is difficult to
enter an accurate input through a finger-touch action;
3. fewer gestures are generally associated with multi-touch gestures that are more familiar. If needed, a small number of menus
and buttons can be used to reduce the number of gestures;
4. duplicated gestures can exist and can be distinguished according to the operation mode.