Cutinf

An infinite size in the dyads f;.3 and f;._3 is replaced
by the signed length of the corresponding axis. For example:

   ] y=: a.{~ (a. i. 'a') + i. 4 5
abcde
fghij
klmno
pqrst
   ((1 2 ,: 2 3) <;.3 y) ; < (1 2 ,: _2 3) <;.3 y
+-----------+-----------+
|+---+---+-+|+---+---+-+|
||abc|cde|e|||fgh|hij|j||
||fgh|hij|j|||abc|cde|e||
|+---+---+-+|+---+---+-+|
||fgh|hij|j|||klm|mno|o||
||klm|mno|o|||fgh|hij|j||
|+---+---+-+|+---+---+-+|
||klm|mno|o|||pqr|rst|t||
||pqr|rst|t|||klm|mno|o||
|+---+---+-+|+---+---+-+|
||pqr|rst|t|||pqr|rst|t||
|+---+---+-+|+---+---+-+|
+-----------+-----------+
   ((0 2 ,: _ 3) <;.3 y) ; < (0 2 ,: __ 3) <;.3 y
+-----------+-----------+
|+---+---+-+|+---+---+-+|
||abc|cde|e|||pqr|rst|t||
||fgh|hij|j|||klm|mno|o||
||klm|mno|o|||fgh|hij|j||
||pqr|rst|t|||abc|cde|e||
|+---+---+-+|+---+---+-+|
+-----------+-----------+