Add 2 fractions works!

mapytex/calculus/core/MO/fraction.py

@@ -46,6 +46,24 @@ class MOFraction(MO):
         self._denominator = denominator
         self.negative = negative
 
+    @property
+    def numerator(self):
+        """ Get the numerator. If self is negative, getting the opposite of the _numerator
+        """
+        if self.negative:
+            return Tree("-", None, self._numerator)
+
+        return self._numerator
+
+    @property
+    def denominator(self):
+        return self._denominator
+
+    def inverse(self):
+        """ return the inverse fraction """
+        return MOFraction(self._denominator,
+                self._numerator, 
+                self.negative)
 
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