code: def min_max_elements(
      backend: pipeline_backend.PipelineBackend, col, stage_name: str
  ):
      col = backend.map(
          col,
          lambda x: (None, (x, x)),
          f"{stage_name}: key by dummy key",
      )  # None is dummy key
      col = backend.reduce_per_key(
          col,
          lambda x, y: (min(x[0], y[0]), max(x[1], y[1])),
          f"{stage_name}: reduce to compute min, max",
      )
      return backend.values(col, "Drop keys")
  
imports: from typing import Type, Dict, Any, Callable, TypeVar, Iterable, List
  from pipeline_dp import pipeline_backend
label_desc: Use image node_id 4 for calling a global function with example usage: min_max_elements(backend, col, stage_name) and returns: backend