Cut504

The dyad x u;.n y
for n
= 1 or _1 or 2 or _2 has been extended as follows:
If x is the atom 0 or 1 ,
it is treated as (#y)#x ; likewise if x is boxed
and >j{x is an atom, it is treated as (j{$y)#>j{x .
For example:

   1 <;.1 i.5 4
+-------+-------+---------+-----------+-----------+
|0 1 2 3|4 5 6 7|8 9 10 11|12 13 14 15|16 17 18 19|
+-------+-------+---------+-----------+-----------+
   (5#1) <;.1 i.5 4
+-------+-------+---------+-----------+-----------+
|0 1 2 3|4 5 6 7|8 9 10 11|12 13 14 15|16 17 18 19|
+-------+-------+---------+-----------+-----------+
   ('';1) <;.1 i.5 4
+--+--+--+--+
| 0| 1| 2| 3|
| 4| 5| 6| 7|
| 8| 9|10|11|
|12|13|14|15|
|16|17|18|19|
+--+--+--+--+
   ('';4#1) <;.1 i.5 4
+--+--+--+--+
| 0| 1| 2| 3|
| 4| 5| 6| 7|
| 8| 9|10|11|
|12|13|14|15|
|16|17|18|19|
+--+--+--+--+