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APL (Dyalog Unicode), 23 bytes Anonymous tacit prefix function. Reuires 0-based indexing (⎕IO←0) (⊢⍪⍨¯1↓⊢,∘↑-∘⍳∘≢↑¨⊢)⊢,⌽ Try it online! ⌽ reverse the argument ⊢, prepend the argument (…) ...
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# [APL (Dyalog Unicode)], 23 bytes <!-- language-all: lang-apl --> Anonymous tacit prefix function. Reuires 0-based indexing (`⎕IO←0`) (⊢⍪⍨¯1↓⊢,∘↑-∘⍳∘≢↑¨⊢)⊢,⌽ [Try it online!][TIO-klr8th27] `⌽` reverse the argument `⊢,` prepend the argument `(`…`)` apply the following tacit function to that:  `⊢` on the characters of the argument  …`↑¨` of each character, take this many characters:   `-∘⍳∘≢` the negative indices \$0…\text{length}-1\$  …`∘↑` mix list of strings into character matrix, then:   `⊢,` prepend the argument (vertically)  `¯1↓` drop the last row  `⊢⍪⍨` append the argument below [APL (Dyalog Unicode)]: https://www.dyalog.com/ [TIO-klr8th27]: https://tio.run/##SyzI0U2pTMzJT///qG@qp/@jtgkG/zUedS161LvqUe@KQ@sNH7VNBnJ1HnXMeNQ2URdE9W4GkZ2LgPxDK4BymmD5nr3/04C6H/X2PepqftS75lHvlkPrjYFqgOYGBzkDyRAPz@D/aQrqHqk5OfnqAA "APL (Dyalog Unicode) – Try It Online"