4.54 - implementing require as a special form.
Including a directory of all code from the book.
Moving query code into place in preparation.
4.55 - simple queries.
4.56 - complex queries.
4.57 - rules.
4.58 - more rules.
4.59 - still more rules.
4.60 - the problems of pairs of answers.

Committing my answer before checking other people's answer. Then adding
a note about how it was solved by another.
4.61 - interesting syntax allowance

I kept thinking of the predicate as a function call, i.e. in the car of
the sexp. But this shows that it doesn't have to be.
4.62 - last-pair query.

Got close but couldn't finish - got the answer from
http://community.schemewiki.org/?sicp-ex-4.62.
4.63 - biblical begats database.

The grandson & son queries were simpler than I originally though.
4.64 - why is Louis Reasoner a crappy developer?
4.65 - why duplicate in wheel results.
4.66 - Ben's accumlation functions.
4.67 - ideas on how to add a loop-detection feature.
Had created several files in the wrong place.
4.68 - reverse query (couldn't figure this one out)

Got the answer from: http://community.schemewiki.org/?sicp-ex-4.68
4.69 - great grandson queries (cheated)

Stumped on this one - grabbed from
http://community.schemewiki.org/?sicp-ex-4.69.

Seems to work but still not quite sure I'm grokking this.
4.70 - finer points of cons-stream.