If f is atomic then f/ on y where y has no items (that is, 0=#y) will attempt to determine the neutral of f . Therefore, in many cases f/y will now give a sensible answer instead of signalling a domain error. For example:

   (+-*)"0/ i.0
0

The process of determining the neutral of atomic f is modelled by the adverb neutral .

neutral=: 1 : 0
 assert. 0 0 -: }. u. b. 0
 c=. __ _ 0 1
 f=. u. ::2:"0
 t=. c (f/ , f~/) 0 1
 assert. ($t) -: 2*(#c),1
 assert. 0 1 e. t
 (t i. 0 1) { ,~c
)

   + neutral
0
   * neutral
1
   >. neutral
__
   (+-*)"0 neutral
0
   ^. neutral
|assertion failure: neutral
|   0 1 e.t