-This summary is relative to the Pintos base code, but we started from
-the reference solution to project 3. Thus, the reference solution runs
-with virtual memory enabled. @xref{Project 3 FAQ}, for the summary
-of project 3.
+This summary is relative to the Pintos base code, but the reference
+solution for project 4 is based on the reference solution to project 3.
+Thus, the reference solution runs with virtual memory enabled.
+@xref{Project 3 FAQ}, for the summary of project 3.
+
+The reference solution represents just one possible solution. Many
+other solutions are also possible and many of those differ greatly from
+the reference solution. Some excellent solutions may not modify all the
+files modified by the reference solution, and some may modify files not
+modified by the reference solution.