
  -spec group_leader() -> pid().

  Returns the process identifier of the group leader for the process
  evaluating the function.

  Every process is a member of some process group and all groups
  have a group leader. All I/O from the group is channeled to the
  group leader. When a new process is spawned, it gets the same
  group leader as the spawning process. Initially, at system
  startup, init is both its own group leader and the group leader
  of all processes.
