Find the preimage under a constant +10 shift: AEFJ : KOPT :: ? : QUVZ

Introduction / Context:
Here the coding rule is a constant Caesar shift of +10. You must reverse the shift to find which input would encode to the given output, practicing inverse reasoning on uniform ciphers.

Given Data / Assumptions:

• AEFJ → KOPT shows +10 for each letter.
• We need ? → QUVZ using the same +10 rule.
• Use modular wrap-around with A=1 … Z=26.

Concept / Approach:
If encoded = original + 10, then original = encoded − 10. Subtract 10 from each of Q, U, V, Z to obtain the preimage.

Step-by-Step Solution:

Verification / Alternative check:
Apply +10 to GKLP → QUVZ, recovering the target perfectly. This confirms the uniform shift assumption and implementation.

Why Other Options Are Wrong:

• GLKP/HKLP/HKQL: Each has at least one letter that fails the exact −10 back-shift from Q, U, V, Z.

Common Pitfalls:
Confusing addition and subtraction or miscounting wrap-around from A or Z. Carefully compute each letter independently.

Final Answer:
GKLP