Olivier Galibert <galibert(a)pobox.com&gt; writes: Then we have to make more of them. Is there any sensible heuristic that could be used here. For instance clear all mark bits. mark with as roots all byte compiled lisp. all strings without properties When we get to objects which we do not want to make read only (i.e. symbols), then either 1. Stick them on some lists as new roots. 2. Mark them with Kyle's "referenced form RO object list". Then dump with the mark bits as they are in addition making each marked object readonly. This from an unfounded guess that most cons pairs at dump time are referenced from byte-compiled lisp.. Jan