Dual · Rats Fighting Over a Burrow (what the solver found)

What the solver found: an exact audit of the classical manuals

13 moves

Rats Fighting Over a Burrow (群鼠争穴) — Elegant Pastime Manual (適情雅趣, 1570), no. 11 At move 6 the book plays He6+; Hc6+ mates just as fast. A dual. The mainline is the book’s solution; a branch, where there is one, is what the solver found. Record from dpxq.com.

Here the book plays He6+. Hc6+ forces mate in the same number of moves. The 排局 tradition tolerates a dual; Western composition counts it as a fault, and it is the commonest one in these books.