How to construct physical zero-knowledge proofs for puzzles with a “single loop” condition

We propose a technique to construct physical Zero-Knowledge Proof (ZKP) protocols for puzzles that require single loop draw feature. Our approach is based on the observation has only one hole and this property remains stable by some simple transformations. Using trick, we can transform big loop, which visible anyone, into solution using transformations do not disclose any information about solution. illustrate our applying it ZKP two Nikoli puzzles: Slitherlink Masyu.