sympy/sympy — pull request #7281 by Tempel (2014-03-16 18:35:09+00:00)
Title: Fix #7206: Equality with matrices.

Equality was changed to support objects with an `_eval_Eq` method. This allows
objects to define alternative algorithms for determining equality. Such a
method was implemented in ImmutableMatrix.

For my previous attempts at fixing this issue, see pull requests #2685 and #2625.