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Concept:
Caesar shift (fixed offset) in the alphabet.
With a +6 shift, each letter moves 6 places forward (mod 26).
This makes JK map to PQ, and JKL map to PQR.
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Example:
JKL → PQR (J→P, K→Q, L→R).
So JK → PQ as part of that shift.
– Brief example: ABC → GHI (A→G, B→H, C→I) under the same +6 shift.