Key Map

Default keymap allow 2 players:

btn(id) function returns true if button is pressed in current frame,
btnp(id) if pressed in current and wasn't pressed in previous frame.

Here a table that summarize the id to interrogate

Action	P1 Key	P1 Id	P2 Key	P2 Id
Up	Arrow Up	0	R	8
Down	Arrow Down	1	F	9
Left	Arrow Left	2	D	10
Right	Arrow Right	3	G	11
A	Z (or <)	4	A	12
B	X (or >)	5	S	13