(though it will be simpler and cheaper to use references)

also, add some (*commented*) memoization debugging output

README pour résumer leur utilisation

scripts de comparaison

variables bound by "let" were not added to the variable map,
provoking an exception, projection symbols were not reused, etc

this fixes a problem with encoding_decorate, where
a parsed Prelude theory contained unneeded "use Tuple2"