Dyadic functions with Rank

Using Catenate (,) we can see that depending on the argument shapes Rank might copy one argument, or not.

      '"' (,⍤1) (4 5⍴⎕A) (,⍤1) '",'
"ABCDE",
"FGHIJ",
"KLMNO",
"PQRST",

      fmt ← {(⍕⍺),': ',⍵}  ⍝ Print ⍺ and join with ': ' to ⍵
      (⍳4) (fmt⍤0 1) 4 5⍴⎕A
0: ABCDE
1: FGHIJ
2: KLMNO
3: PQRST