Break up the 'someos' docs classification based on a more user-focused scheme, including creation of a separate 'Concurrent Execution' section
diff --git a/Doc/library/concurrency.rst b/Doc/library/concurrency.rst
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+.. _concurrency:
+
+********************
+Concurrent Execution
+********************
+
+The modules described in this chapter provide support for concurrent
+execution of code. The appropriate choice of tool will depend on the
+task to be executed (CPU bound vs IO bound) and preferred style of
+development (event driven cooperative multitasking vs preemptive
+multitasking) Here's an overview:
+
+
+.. toctree::
+
+ threading.rst
+ multiprocessing.rst
+ concurrent.futures.rst
+ subprocess.rst
+ sched.rst
+ queue.rst
+ select.rst
+
+
+The following are support modules for some of the above services:
+
+.. toctree::
+
+ dummy_threading.rst
+ _thread.rst
+ _dummy_thread.rst