1. A Companion to the Summa by Walter Farrell O.P.
another link:
A Companion to the Summa
2. A Tour of the Summa by Paul J. Glenn
Also, these works can be found in print versions: A Companion to the Summa, generally found used and in 4 volumes, and A Tour of the Summa, in a single volume, both new and used.
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