CATALOGUE (1) {y forms a catalogue from the atoms of its arguments, its shape being the chain of the shapes of the opened items of y, and the common shape of the boxed results is $y. The case {a;<b is called the Cartesian product of a and b. Thus:
c=. {'ht';'ao';'gtw'
n=. { 10 11 ; i.2 3
c n
+---+---+---+ +----+----+----+
|hag|hat|haw| |10 0|10 1|10 2|
+---+---+---+ +----+----+----+
|hog|hot|how| |10 3|10 4|10 5|
+---+---+---+ +----+----+----+
+---+---+---+ +----+----+----+
|tag|tat|taw| |11 0|11 1|11 2|
+---+---+---+ +----+----+----+
|tog|tot|tow| |11 3|11 4|11 5|
+---+---+---+ +----+----+----+
$c $n
2 2 3 2 2 3
FROM (0 _) If x is an integer in the range from ΓÇô#y to <:#y, then x{y selects item (#y)|x from y. More generally, x may be a boxed list, whose successive elements are (possibly) boxed lists that specify selection along successive axes of y. For example:
y 2 0{y
abcdef mnopqr
ghijkl abcdef
mnopqr
(<2 0){y (<2 0;1 3){y
m np
bd
Finally, if any r=.>j{>x used in the selection is itself boxed, selection is made by the indices along that axis (i.j{$y) that do not occur in >r. For example: