Guy Steele, graph theory, & self-referential data structures

To all CL & Scheme hackers,

I recall coming across a very interesting article by Guy Steele, where
he explores some of the ramifications of the interplay in the external
representation of self-referential data structures and graph theory in
CL and/or Scheme. Does anybody have a pointer to where I might find
this?

Many thanks,

~Tomer


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