code: func (iter Enumerator) ParallelSelect(operation Transform) Enumerator {
  	if cpus := runtime.NumCPU(); cpus != 1 {
  		intermediate := iter.splitN(operation, uint(cpus))
  		return intermediate[0].Merge(intermediate[1:]...)
  	}
  	return iter
  }
docs: // ParallelSelect will execute a Transform across all logical CPUs available to the current process.