NB. from stdlib.ijs
toupper=: 3 : 0`((((65+i.26){a.)(97+i.26)}a.) {~ a. i. ])@.(2 = 3!:0)
x=. I. 26 > n=. ((97+i.26){a.) i. t=. ,y
($y) $ ((x{n) { (65+i.26){a.) x}t
)