continue refactoring to optimize for mtl

mtl/test_ast.py

@@ -0,0 +1,31 @@
+import mtl
+from mtl.hypothesis import MetricTemporalLogicStrategy
+
+from hypothesis import given
+
+
+@given(MetricTemporalLogicStrategy)
+def test_identities(phi):
+    assert mtl.TOP == mtl.TOP | phi
+    assert mtl.BOT == mtl.BOT & phi
+    assert mtl.TOP == phi | mtl.TOP
+    assert mtl.BOT == phi & mtl.BOT
+    assert phi == phi & mtl.TOP
+    assert phi == phi | mtl.BOT
+    assert mtl.TOP == mtl.TOP & mtl.TOP
+    assert mtl.BOT == mtl.BOT | mtl.BOT
+    assert mtl.TOP == mtl.TOP | mtl.BOT
+    assert mtl.BOT == mtl.TOP & mtl.BOT
+    assert ~mtl.BOT == mtl.TOP
+    assert ~mtl.TOP == mtl.BOT
+    assert ~~mtl.BOT == mtl.BOT
+    assert ~~mtl.TOP == mtl.TOP
+    assert (phi & phi) & phi == phi & (phi & phi)
+    assert (phi | phi) | phi == phi | (phi | phi)
+    assert ~~phi == phi
+
+
+def test_walk():
+    phi = mtl.parse(
+        '(([ ][0, 1] ap1 & < >[1,2] ap2) | (@ap1 U ap2))')
+    assert len(list((~phi).walk())) == 11