Square: 3x3 keypad mapped to geometric elements of a square

We introduce Square, a text entry device in the form of a small square button. Conceptually, it is equivalent to a 3times3 keypad since the nine geometric elements of a square - four vertices, four edges, and a face - play the part of the nine keys of a 3times3 keypad. Being small and simple, Square can allow more freedom to the design of a mobile device. In addition, it is better for blind typing than a keypad due to the distinct tactile properties of the different elements of a square button.