; Subneg (Subtract and Branch if Negative) — OISC sibling of Subleq
; Instruction: a b c
;   mem[b] -= mem[a]
;   if mem[b] < 0: jump to address c
;   else: advance to next instruction
;
; Program: copy the value at address A into address B
; Symbolic addresses: zero=10, A=11, B=12, tmp=13
; Initial values: A=7, B=0, zero=0, tmp=0

; Clear zero register (idempotent: 0 -= 0 = 0)
10 10 1
; Negate A into tmp  (tmp = 0 - 7 = -7, negative => branch to 2)
11 13 2
; Clear B            (B = 0 - 0 = 0, not negative => fall through)
10 12 3
; Copy: B -= tmp     (B = 0 - (-7) = 7, not negative => fall through)
13 12 4
; halt (address 4 — no instruction, execution stops)
; data: 10:0  11:7  12:0  13:0