Quick issue -- there are many grades of levels 2 and 3 on that matrix (i.e. one could know what a red-black tree is and where it should be used -- or one could

Quick issue -- there are many grades of levels 2 and 3 on that matrix (i.e. one could know what a red-black tree is and where it should be used -- or one could easily be able to implement it; one could know basic scheme -- tail recursion, continuations -- or one could have made a prolog compiler on top of common lisp (cf Norvig's book)). In essence to put it this way: "for $thing in ( technology, pattern, algorithm, methodology ): it doesn't discriminate someone who've toyed with a $thing, someone who has made an implementation of that $thing for an employer or someone who has authored an all-new $thing."