y=: 7 8$ '0123456789',a.{~ ,65 97+/i.26
   y
01234567
89ABCDEF
GHIJKLMN
OPQRSTUV
WXYZabcd
efghijkl
mnopqrst

   (1 2 ,: 3 999) [;.0 y
ABCDEF
IJKLMN
QRSTUV
   (1 2 ,: 3 _) [;.0 y
ABCDEF
IJKLMN
QRSTUV

   (1 2 ,: _999 3) [;.0 y
opq
ghi
YZa
QRS
IJK
ABC
   (1 2 ,: _ 3) [;.0 y
ABC
IJK
QRS
YZa
ghi
opq

   <"2 x=: 1 2 ,:"1 > ,"2 { ;~"1 ] _ __ ,. 3
+-----+----+----+---+
|1 2  |1 2 |1 2 |1 2|
|_ _  |_ 3 |3 _ |3 3|
+-----+----+----+---+
| 1  2| 1 2|1  2|1 2|
|__ __|__ 3|3 __|3 3|
+-----+----+----+---+
   x <;.0 y
+------+---+------+---+
|ABCDEF|ABC|ABCDEF|ABC|
|IJKLMN|IJK|IJKLMN|IJK|
|QRSTUV|QRS|QRSTUV|QRS|
|YZabcd|YZa|      |   |
|ghijkl|ghi|      |   |
|opqrst|opq|      |   |
+------+---+------+---+
|tsrqpo|opq|FEDCBA|ABC|
|lkjihg|ghi|NMLKJI|IJK|
|dcbaZY|YZa|VUTSRQ|QRS|
|VUTSRQ|QRS|      |   |
|NMLKJI|IJK|      |   |
|FEDCBA|ABC|      |   |
+------+---+------+---+

   <"2 x=: _1 2 ,:"1 > ,"2 { ;~"1 ] _ __ ,. 3
+-----+----+-----+----+
|_1 2 |_1 2|_1 2 |_1 2|
| _ _ | _ 3| 3 _ | 3 3|
+-----+----+-----+----+
|_1  2|_1 2|_1  2|_1 2|
|__ __|__ 3| 3 __| 3 3|
+-----+----+-----+----+
   x <;.0 y
+------+---+------+---+
|234567|234|YZabcd|YZa|
|ABCDEF|ABC|ghijkl|ghi|
|IJKLMN|IJK|opqrst|opq|
|QRSTUV|QRS|      |   |
|YZabcd|YZa|      |   |
|ghijkl|ghi|      |   |
|opqrst|opq|      |   |
+------+---+------+---+
|tsrqpo|opq|dcbaZY|YZa|
|lkjihg|ghi|lkjihg|ghi|
|dcbaZY|YZa|tsrqpo|opq|
|VUTSRQ|QRS|      |   |
|NMLKJI|IJK|      |   |
|FEDCBA|ABC|      |   |
|765432|234|      |   |
+------+---+------+---+