coalg: Make 'graph' subcommand more cli-friendly

- Read only one formula, we also only generate one graph
- Don't print a prompt or the satisfiability result

This allows to redirect the output graph to a file or directly to dot.

src/coalg/coalg.ml

@@ -188,7 +188,11 @@ let choiceNNF () =
     with End_of_file -> ()
 
 let choiceGraph () =
-  choiceSat ();
+  let sorts = (FE.sortTableFromString Sys.argv.(2)) in
+
+  let input = read_line () in
+  let (tbox, f) = CoAlgFormula.importQuery input in
+  ignore(CoAlgReasoner.isSat sorts nomTable tbox f);
   print_endline (CM.graphToDot ())
 
 let choiceVerify () =