Based on the GitHub issue, I can see this is about the `uniq` function in `sympy/utilities/iterables.py`. The issue mentions lines 2109-2124. Let me create a patch based on the problem description.

The issue is that when iterating over `uniq(f)` and modifying the list `f` simultaneously, the output is silently wrong. The fix should check if the size of a mutable sequence changes during iteration and raise a `RuntimeError` similar to what Python does with dictionaries/sets.

Based on the issue description and standard Python patterns for `uniq` functions, here's the patch:

--- a/sympy/utilities/iterables.py
+++ b/sympy/utilities/iterables.py
@@ -2106,6 +2106,7 @@ def uniq(seq, result=None):
     >>> list(googol)
     []
     """
+    initial_len = None
     try:
         seen = set()
         result = result or []
@@ -2113,6 +2114,12 @@ def uniq(seq, result=None):
             if item not in seen:
                 seen.add(item)
                 result.append(item)
+                if initial_len is None:
+                    try:
+                        initial_len = len(seq)
+                    except TypeError:
+                        pass
+                if initial_len is not None and len(seq) != initial_len:
+                    raise RuntimeError("dictionary changed size during iteration")
                 yield item
     except TypeError:
         if item not in result: