FACT: MOV R1, -(R6)  ; save registers
         MOV R2, -(R6)
	 MOV #3, R0     ; calculating address of parameter:
	 ADD R6, R0
         MOV@ R0, R1    ; parameter
         MOV# 2, R2
         CMP R2, R1     ; if x >= 2, do the longer part below
         BGE RECURSE
         MOV# 1, R0     ; return value is 1
    RET: MOV (R6)+, R2  ; restore
         MOV (R6)+, R1  ; restore
         RTS 
RECURSE: DEC R1         ; x-1
         MOV R1, -(R6)  ; push parameter for recursive call
         JSR FACT
         INC R6         ; un-push
         INC R1         ; get x back
         MUL R1, R0     ; R0 becomes x*fact(x-1)
         BR RET