At the bottom of this essay, there is discussion about identity functions and
how they interact with the / adverb.
http://www.jsoftware.com/jwiki/PascalJasmin/nil_and_empty_in_J
+/ (i.0) , i.0
0
*/ (i.0) , i.0
1
(+/ (i.0) , i.0) -: +/ i.0
1
if u/ 0$0 is defined, then so should (0$0) u y or x u 0$0 or (0$0) u 0$0.
the equivalent definitions are: (u/ (0$0)) u y and x u u/ 0$0 and (u/ 0$0) u
u/ 0$0
currently x + empty returns empty:
$ 3 + i.0
0
+/ 3
3
which doesn't make sense if an identity function has been defined for +
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