helper for infer_columns. removes paths that are direct children of the n-1 or n-2 path

def eliminate_sequential_children(paths):
  "helper for infer_columns. removes paths that are direct children of the n-1 or n-2 path"
  return [p for i,p in enumerate(paths) if not ((i>0 and paths[i-1]==p[:-1]) or (i>1 and paths[i-2]==p[:-1]))]