The Logic Book, M. Bergmann, J. Moor, J. Nelson, McGraw Hill, 2004, 10.6E, 2(a), p. 572

As usual, we prove the validity of the argument.

1. a = b • ¬ Bab
2. ∴¬ (x)Bxx
3. a = b ......... 1 Simp.
4. ¬ Bab ......... 1 Simp.
5. ¬ Baa ......... 3,4 Id
6. (∃x)¬ Bxx ......... 5 EG
7. ¬ (x)Bxx ......... 6 QC