[avmich]

Had a kind of opposite experience with K.

J seems quite reasonable - intuitively - after reading very good "J for C programmers" (http://jsoftware.com/help/jforc/contents.htm) . And symbols in J chosen for most operations also seem good - at least after some small use. "NB." is immediately "nota bene" (I guess knowing some Latin doesn't hurt - it's "note well", but I always understand it as "note that") - don't some other languages use this acronym for comments as well?

What is IMO particularly good in K is the small size of the interpreter. J is "for the whole math", while K is "for practical 99% of cases" - at least it feels like that. Having small interpreter which fits in CPU cache allows potentially to run faster than with assembler, because K code is packed densely - so less time to wait for slow memory.