AFAIK Arel is not a real algreba, since it does not really allow composing relations the way we want. More info here: http://www.try-alf.org/blog/2013-10-21-re

AFAIK Arel is not a real algreba, since it does not really allow composing relations the way we want. More info here: http://www.try-alf.org/blog/2013-10-21-relations-as-first-class-citizen http://www.try-alf.org/blog/2013-10-21-relations-as-first-cl...