message: Address nits in prolog prototype readme
diff: @@ -6,26 +6,29 @@ flow of data during static checking, and to test the reading of real data.
  ## Setup
  -To run the code you will need to install [SWI-Prolog][swi_prolog].
  +To run the code you will need to install [SWI-Prolog][swi-prolog].
  This package can be found on many distributions; on Ubuntu it can be
  installed with `sudo apt-get install swi-prolog`.
  -[swi_prolog]: http://www.swi-prolog.org/
  +[swi-prolog]: http://www.swi-prolog.org/
  ## Running the examples
  In the shell, change to the `src` directory then start the interpreter with:
  ```sh
  -$ chdir src
  -$ swipl load.pl
  +cd src
  +swipl load.pl
  ```
  +
  The full suite of examples can be run with:
  ```prolog
  ?- run.
  ```
  +
  or individual examples can be run with:
  +
  ```prolog
  ?- runtest(Name). % e.g. runtest(sudoku).
  ```
  @@ -37,20 +40,25 @@ of a test case, only that there are no more test cases.
  ## Tracing Prolog execution
  Tracing can be switched on in SWI-Prolog by entering the following:
  +
  ```prolog
  ?- trace.
  ```
  +
  This will execute the next goal in trace mode.
  A more convenient way to start debugging is to set a spy point on
  the predicate you are interested in. The goal:
  +
  ```prolog
  ?- spy(repr/4).
  ```
  +
  sets a spy point on the `repr/4` predicate (that is, the predicate named
  `repr` which has four arguments), and also puts Prolog into debug mode.
  In subsequent goals, execution will stop when it hits a "port" of the
  predicate. For example:
  +
  ```prolog
  ?- spy(repr/4).
  % Spy point on repr/4
  @@ -60,18 +68,20 @@ true.
  Test: xyz
  * Call: (9) repr([], [], sigma(x, int(16, eint(-32768), eint(32767)), sigma(y, int(16, eint(-32768), eint(32767)), sigma(z, int(16, eint(-32768), eint(32767)), unit))), _G453) ?
  ```
  +
  The first port shown here is the `Call` port, which shows the instantiation
  of `repr/4` at the time it is first called. The `_G453` argument represents
  something that is not yet instantiated.
  -At the `?` prompt you can hit 'c' (or space/return) to "creep" to the next
  -port, or hit 's' to skip to the end. Type '?' for a list of other commands.
  +At the `?` prompt you can hit `c` (or space/return) to "creep" to the next
  +port, or hit `s` to skip to the end. Type `?` for a list of other commands.
  Since Prolog execution can involve backtracking, debuggers use a "4-port"
  model of tracing. Aside from the expected `Call` and `Exit` ports, there
  are also `Redo` and `Fail` ports, which indicate that we are re-entering
  a goal for more solutions, and that we have exhausted all solutions,
  respectively. SWI-Prolog additionally has ports `Unify` and `Exception`;
  -see http://www.swi-prolog.org/pldoc/man?section=debugoverview for more
  +see [the documentation][debug-docs] for more
  information.
  +[debug-docs]: http://www.swi-prolog.org/pldoc/man?section=debugoverview
  