Made this code clearer.

Author: ischurov

pandas/tseries/index.py

@@ -1293,12 +1293,11 @@ def _parsed_string_to_bounds(self, reso, parsed):
 
     def _partial_date_slice(self, reso, parsed, use_lhs=True, use_rhs=True):
         is_monotonic = self.is_monotonic
-        if ((reso in ['day', 'hour', 'minute'] and
-             not (self._resolution < Resolution.get_reso(reso) or
-                  not is_monotonic)) or
-            (reso == 'second' and
-             not (self._resolution <= Resolution.RESO_SEC or
-                  not is_monotonic))):
+        if (is_monotonic
+            and ((reso in ['day', 'hour', 'minute']
+                  and self._resolution >= Resolution.get_reso(reso))
+                 or (reso == 'second'
+                     and self._resolution > Resolution.RESO_SEC))):
             # These resolution/monotonicity validations came from GH3931,
             # GH3452 and GH2369.
             raise KeyError