Problem: Duplicate characters

Code: Duplicate+characters/tails_1642045013

Nibbles version: 0.2 | 0.21 | 0.22 | 0.23 | 0.24 | 0.25 | 1.00

Format: Compact | Simple | +Type | Table | JSON | .nbl (DeBruijn) | .nbl (names)

(implicit string concatenation) 
    + (concat) 
        . (map) 
            @ (= fstLine) 
            ^ (replicate) <--arg( A ) 
                2 (integer) 
                $ (= A) 
    "\n" (string)