add PAPNI to top level imports and one vpa benchmark model

Author: emuskardin

DotModels/arithmetics.dot

@@ -0,0 +1,10 @@
+digraph learnedModel {
+s0 [label="s0", shape=circle];
+s1 [label="s1", shape=doublecircle];
+s0 -> s1  [label="1"];
+s0 -> s0  [label="push(()"];
+s1 -> s0  [label="+"];
+s1 -> s1  [label=") / pop(()"];
+__start0 [label="", shape=none];
+__start0 -> s0  [label=""];
+}

aalpy/__init__.py

@@ -37,6 +37,7 @@
     run_non_det_Lstar,
     run_RPNI,
     run_stochastic_Lstar,
+    run_PAPNI
 )
 from .oracles import (
     BreadthFirstExplorationEqOracle,

aalpy/utils/BenchmarkVpaModels.py

@@ -415,7 +415,7 @@ def step(self, letter):
 
     sul = ArithmeticSUL()
 
-    alphabet = VpaAlphabet(internal_alphabet=['1', '+', '-', '/', '0'], call_alphabet=['(', ], return_alphabet=[')', ])
+    alphabet = VpaAlphabet(internal_alphabet=['1', '+',], call_alphabet=['(', ], return_alphabet=[')', ])
     merged_alphabet = alphabet.get_merged_alphabet()
     data = []
     while len(data) < num_sequances: