Why does 'The Reasoned Schemer' add an 'o' to the end of its functions?

Question

In the reasoned schemer, they name standard lisp functions with an 'o' on the end, eg conso and appendo.

My question is: Why does 'The Reasoned Schemer' add an 'o' to the end of its functions?

Answer 1

From page 2 of http://www.cs.indiana.edu/~eholk/papers/sfp2012.pdf:

It is conventional in Scheme for the names of predicates to
end with the ‘?’ character. We have therefore chosen to end the
names of miniKanren goals with a superscript o, which is meant
to resemble the top of a ?. The superscript e in conde
stands for
‘every,’ since every conde clause may contribute answers.