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+# MEM
+16^2 sized shared program and heap memory
+16^2 sized stack
+16^2 sized return stack
+
+input data is a single short at __0xbffe__
+
+screen data is 8-bit indexed on two layers
+(one short is two pixels, one for each layer), and located
+__from 0xbfff to 0xffff__
+
+# OPS
+NOP    ( -- ) sit back and do nothing
+LIT x  ( -- x ) push x to top of the stack
+POP    ( a -- ) remove top of the stack
+NIP    ( a b -- b ) remove second value from top of the stack
+SWP    ( a b -- b a ) swap top two values of the stack
+ROT    ( a b c -- b c a ) rotates top three values of the stack to the left
+DUP    ( a -- a a ) duplicates top of the stack
+OVR    ( a b -- a b a ) duplicates second value at the top of the stack
+EQU    ( a b -- bool ) push 0001 if a == b, 0000 otherwise
+NEQ    ( a b -- bool ) push 0001 if a != b, 0000 otherwise
+GTH    ( a b -- bool ) push 0001 if a > b, 0000 otherwise
+LTH    ( a b -- bool ) push 0001 if a < b, 0000 otherwise
+JEZ x  ( cond -- ) conditional jump to x if cond != 0
+JNZ x  ( cond -- ) conditional jump to x if cond == 0
+JMP x  ( -- ) jump to x
+JRT x  ( -- ) jump to x and store PC+2 to return stack
+RET    ( -- ) return from call, or quit if not in call
+LDA    ( addr -- value ) push value at absolute address to top of the stack
+STA    ( val addr -- ) write a value to an absolute address
+RED    ( -- value ) read byte from stdin
+WRT    ( value -- ) write byte to stdout
+ADD    ( a b -- a+b )
+SUB    ( a b -- a-b )
+MUL    ( a b -- a*b )
+DIV    ( a b -- a/b )
+AND    ( a b -- a&b )
+ORA    ( a b -- a|b )
+XOR    ( a b -- a^b )
+LSF    ( a shift -- c ) left shift
+RSF    ( a shift -- c ) right shift
+SLP    ( -- ) give control back to the interpreter
+INC    ( a -- a+1 )
+DEC    ( a -- a-1 )
+DBG    ( -- ) output debug informations, can be omitted in release builds