Add a sequence diagram for the chained coroutines example
diff --git a/Doc/library/asyncio-task.rst b/Doc/library/asyncio-task.rst
index afcfea8..8361257 100644
--- a/Doc/library/asyncio-task.rst
+++ b/Doc/library/asyncio-task.rst
@@ -74,7 +74,6 @@
loop = asyncio.get_event_loop()
loop.run_until_complete(greet_every_two_seconds())
-
.. seealso::
:ref:`Hello World example using a callback <asyncio-hello-world-callback>`.
@@ -104,6 +103,16 @@
``compute()`` is chained to ``print_sum()``: ``print_sum()`` coroutine waits
until ``compute()`` is completed before returing its result.
+Sequence diagram of the example:
+
+.. image:: tulip_coro.png
+ :align: center
+
+The diagram shows the logical links between the task and the two coroutines, it
+does not describe exactly how things work internally. For example, the sleep
+coroutine creates an internal future which uses
+:meth:`BaseEventLoop.call_later` to wake up the task in 1 second.
+
InvalidStateError
-----------------
diff --git a/Doc/library/tulip_coro.dia b/Doc/library/tulip_coro.dia
new file mode 100644
index 0000000..c4e19a0
--- /dev/null
+++ b/Doc/library/tulip_coro.dia
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diff --git a/Doc/library/tulip_coro.png b/Doc/library/tulip_coro.png
new file mode 100644
index 0000000..e083bc3
--- /dev/null
+++ b/Doc/library/tulip_coro.png
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