+ if (!params->id && params->w == 3) {
+ /*
+ * We can't have a 3x3 puzzle without an identity either,
+ * because 3x3 puzzles can't ever be harder than Trivial
+ * (there are no 3x3 latin squares which aren't also valid
+ * group tables, so enabling group-based deductions doesn't
+ * rule out any possible solutions) and - as above - Trivial
+ * puzzles can't not have an identity.
+ */
+ return "3x3 puzzles must have an identity";
+ }