Topology.contacts_between: def of bend-prot@0.1.0.0
Import: import bend-prot@0.1.0.0/topology.bend as Topology
Lines 90-97 of bend-prot@0.1.0.0/topology.bend: https://jend.leeeet.dev/read.txt?path=bend-prot@0.1.0.0/topology.bend&start_line=90&end_line=97

import Base
import bend-prot@0.1.0.0/protein.bend as P

# Interface size: pairs (x in xs, y in ys) with dist2 < c2. Consumes xs once;
# ys is reusable so every head reuses it (reference counted).
def contacts_between(xs: List<&2, P.Atom>, +ys: List<&2, P.Atom>, +c2: F32) -> Nat:
  match xs:
    case Nil{}:
      0n
    case h <> t:
      Nat.add(contacts_between(t, ys, c2), contacts_of_head(h, ys, c2))

Uses (6):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=F32
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=List
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Nat.add
  https://jend.leeeet.dev/definition.txt?path=bend-prot@0.1.0.0/protein.bend&name=Atom
  https://jend.leeeet.dev/definition.txt?path=bend-prot@0.1.0.0/topology.bend&name=contacts_of_head