static long stupidFib_collab(ICollab collab, int n) {
  ret collab_computeLong2(collab,
    receiver -> stupidFib_collab(collab, n, receiver));
}

svoid stupidFib_collab(ICollab collab, int n, LongConsumer continuation) {
  // switch to serial if small enough work unit
  if (n < 24) ret stupidFib(n);
  
  // recursion base
  if (n < 3) ret with continuation.accept(1L);
  
  // recursion step
  var collector = longPairCollector((a, b) -> continuation.accept(a+b));
  collab.addWork(-> stupidFib_collab(collab, n-1, collector.setterForA()));
  collab.addWork(-> stupidFib_collab(collab, n-2, collector.setterForB()));
}