[plt-scheme] Alpha-beta pruning

I am trying to implement the alpha beta pruning but with no luck can anyone
help me with how it works I am trying to use this Algorithm

αβ(n, d, α, β)
S ← Successors(n)
if d ≤ 0 ∨ S ≡ ∅ then
return f(n)
best ← −∞
for all ni ∈ S do
  v ← −αβ(ni, d − 1, −β, −max(α, best))
   if    v > best    then
    best ← v if    best ≥ β    then
      return best
return best


Best regards,
G
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