message: Point to TLA+ documentation that doesn't confuse learners with PlusCal.
diff: @@ -16,7 +16,7 @@ CCF implements various modifications to Raft as it was originally proposed by On
  The TLA+ specification models the intended behavior of Raft as it is modified for CCF. Below, we explain several core parts of the specification in more detail.
  -You can find the full specification in the :ccf_repo:`tla/` directory and more information on TLA+ `here <http://lamport.azurewebsites.net/tla/tla.html>`_. Several good resources exist online, one good example is `this guide <https://www.learntla.com>`_.
  +You can find the full specification in the :ccf_repo:`tla/` directory and more information on TLA+ `here <http://lamport.azurewebsites.net/tla/tla.html>`_. Several good resources exist online, one good example is Lamport's `Specifying Systems <https://lamport.azurewebsites.net/tla/book.html>`_.
  Running the model checker
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