type
  NodeKind = enum opValue, opAdd, opSub, opMul, opCall
  Node = ref object
     case k: NodeKind
     of opValue: value: int
     of opAdd, opSub, opMul, opCall: kids: seq[Node]

proc safeLen(n: Node): int = if n.k == opValue: 0 else: n.kids.len

proc sameTree(a, b: Node): bool =
  if a.k == b.k:
    if a.k == opValue: result = a.value == b.value
    elif a.kids.len == b.kids.len:
      result = true
      for i in 0..<a.kids.len:
         if not sameTree(a.kids[i], b.kids[i]): return false

proc containsSubtree(n, subtree: Node): bool =
  if sameTree(n, subtree): return true
  for i in 0 .. <n.safeLen:
    if n.kids[i].containsSubtree(subtree): return true