Dyalog Forums

. . . {⍵,[-.1]'.^'[0>⎕NC⍪⍵]}⎕UCS 192+⍳64
ÀÁÂÃÄÅÆÇÈÉÊËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿ
.......................^......^........................^.....^.^
Obviously there's no mystery in the × and ÷ flagged above, though how they got in those positions in the first place seems a bit odd. But why do capital Thorn and those two wyes not qualify?

The precise answer to this is lost in the fog of the old pre-Unicode fonts; these symbols are allowed in order to allow old code to continue to work, only. Dyalog strongly advises you not to use any of these characters in names, as they are bound to cause problems in the future as inter-operability between APL and other programming languages becomes more and more important.

APL# (a new dialect of Dyalog APL, which we will "soon" start discussing specifications for in public) will not allow the use of these characters in identifiers.