ab:3 3#"abcdefghi"
("abc"
"def"
"ghi")
dd:3 3#"012345678"
("012"
"345"
"678")
ab,dd
"ghi"
"012"
+ab,dd / flip (transpose) join
("adg036"
"beh147"
"cfi258")
ab,'dd / eachpair join
("abc012"
"def345"
"ghi678")
+(+ab),dd
("abc036"
"def147"
"ghi258")