lib/dydx/algebra/formula.rb in dydx-0.0.7 vs lib/dydx/algebra/formula.rb in dydx-0.0.8

@@ -28,29 +28,30 @@
       alias_method :d, :differentiate
 
       def to_s
         if (multiplication? && (f.is_minus1? || g.is_minus1?)  )
           "( - #{g.to_s} )"
-        elsif multiplication? && g.divisor?
+        elsif multiplication? && g.inverse?(:*)
           "( #{f.to_s} / #{g.x.to_s} )"
-        elsif multiplication? && f.divisor?
+        elsif multiplication? && f.inverse?(:*)
           "( #{g.to_s} / #{f.x.to_s} )"
-        elsif addition? && g.subtrahend?
+        elsif addition? && g.inverse?(:+)
           "( #{f.to_s} - #{g.x.to_s} )"
-        elsif addition? && f.subtrahend?
+        elsif addition? && f.inverse?(:+)
           "( #{g.to_s} - #{f.x.to_s} )"
         else
           "( #{f.to_s} #{@operator} #{g.to_s} )"
         end
       end
 
       def include?(x)
         f == x || g == x
       end
 
-      def openable?(x)
-        x.is_num? && (f.is_num? || g.is_num?)
+      def openable?(operator, x)
+        distributive?(self.operator, operator) &&
+        (f.combinable?(x, operator) || g.combinable?(x, operator))
       end
 
       # TODO: interchangeable
       def ==(x)
         to_s == x.to_s
@@ -73,6 +74,6 @@
         @f, @g = @g, @f
         self
       end
     end
   end
-end
\ No newline at end of file
+end