+If necessary
+(see below),
+.B dump-runlisp-image
+invokes each selected Lisp in order to determine a
+.IR "version hash" .
+For each selected Lisp system,
+it constructs a command line,
+in the manner of
+.BR runlisp (1),
+to evaluate the expression resulting from expanding the
+.B lisp-version
+setting in the Lisp system's configuration section.
+It hashes the result,
+using a collision-resistant hash function
+(currently SHA256),
+to produce a string of hexadecimal digits which represents
+the versions of the various pieces of Lisp code which
+.I should
+be in the dumped image.
+The standard setting for
+.B lisp-version
+includes the Lisp implementation version string
+and the version of ASDF currently installed.
+(This step is skipped
+if it's not necessary to determine the Lisp system versions.
+In practice, this happens when the
+.RB ` \-r ',
+.RB ` \-R '
+and
+.RB ` \-U '
+options are all set.)
+.PP