Add Creating A PID as an elixir til

elixir/creating-a-pid.md

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+# Creating A PID
+
+Often times, when invoking a function that spawns a process, the PID of the
+spawned process is returned and we bind to it. That PID is a reference to
+some BEAM process in our system.
+
+We can create our own references using the `pid/3` function.
+
+Let's assume we have the following processes, among others, in our system at
+the moment.
+
+```elixir
+> Process.list |> Enum.reverse |> Enum.take(3)
+[#PID<0.284.0>, #PID<0.283.0>, #PID<0.282.0>]
+```
+
+We can create a reference to any of them using the three number parts that
+they are made up of.
+
+```elixir
+> pid(0, 284, 0)
+#PID<0.284.0>
+```
+
+See, it's alive.
+
+```elixir
+> pid(0, 284, 0) |> Process.alive?
+true
+```
+
+What if we make up a PID that doesn't actually reference any process?
+
+```elixir
+> pid(0, 333, 0) |> Process.alive?
+false
+```
+
+Note: there is also a `pid/1` version of the function. See `h pid` for more
+details.