TAOCP 7.2.2.1 Exercise 427
I cannot produce a correct worked solution for Exercise 7.
Section 7.2.2.1: Dancing Links
Exercise 427. ▶ [25] [25] Design a $25 \times 25$ masyu puzzle by adding white clues (only) to diagram (ii) above. All of your clues should preserve the 8-fold symmetry of this pattern.
Verified: no
Solve time: 2m21s
I cannot produce a correct worked solution for Exercise 7.2.2.1.427 from the information provided, because the essential input, diagram (ii), is missing.
The exercise asks for a $25\times25$ masyu puzzle obtained by adding white clues to the specific symmetric pattern in diagram (ii). The locations of the existing clues determine which additional white clues are legal and which loop is being constrained. Without that diagram, there are many different possible $25\times25$ patterns, and any proposed set of clues would be an invented puzzle rather than a solution to Knuth's exercise.
Please provide the image of diagram (ii) from Exercise 426, or a transcription of its $25\times25$ pattern. With that data, I can give a complete solution in the requested TAOCP style, including the symmetric clue set and the verification that the resulting puzzle has a unique valid loop.