# sympy__sympy-16106
# Loki Mode Multi-Agent Patch
# Attempts: 1

Based on the issue description and the architect's analysis, I can generate a patch that adds the missing `_print_Indexed` and `_print_IndexedBase` methods to the MathML printer. The error shows the code structure and the fix is straightforward based on the traceback.

```
--- a/sympy/printing/mathml.py
+++ b/sympy/printing/mathml.py
@@ -1,6 +1,7 @@
 """
 A MathML printer.
 """
+from sympy.core.compatibility import default_sort_key
 
 from __future__ import print_function, division
 
@@ -152,6 +153,22 @@ class MathMLPresentationPrinter(MathMLPrinterBase):
         mrow.appendChild(mo)
         return mrow
 
+    def _print_Indexed(self, e):
+        msub = self.dom.createElement('msub')
+        msub.appendChild(self._print(e.base))
+        if len(e.indices) == 1:
+            msub.appendChild(self._print(e.indices[0]))
+        else:
+            mrow = self.dom.createElement('mrow')
+            for i, idx in enumerate(e.indices):
+                if i > 0:
+                    mo = self.dom.createElement('mo')
+                    mo.appendChild(self.dom.createTextNode(','))
+                    mrow.appendChild(mo)
+                mrow.appendChild(self._print(idx))
+            msub.appendChild(mrow)
+        return msub
+
+    def _print_IndexedBase(self, e):
+        return self._print(e.label)
+
     def _print_Mul(self, expr):
 
         def multiply(expr, mrow):
@@ -354,6 +371,22 @@ class MathMLContentPrinter(MathMLPrinterBase):
             x.appendChild(self._print(arg))
         return x
 
+    def _print_Indexed(self, e):
+        x = self.dom.createElement('apply')
+        x_1 = self.dom.createElement('csymbol')
+        x_1.appendChild(self.dom.createTextNode('subscript'))
+        x.appendChild(x_1)
+        x.appendChild(self._print(e.base))
+        for idx in e.indices:
+            x.appendChild(self._print(idx))
+        return x
+
+    def _print_IndexedBase(self, e):
+        x = self.dom.createElement('ci')
+        x.appendChild(self.dom.createTextNode(self.doprint(e.label)))
+        return x
+
     def _print_MatrixBase(self, m):
         x = self.dom.createElement('matrix')
         for i in range(m.rows):
```