Grid technique · Intermediate
Two-Bridge Elimination
If nothing in a third category can connect two items, they cannot be paired with each other.
Why it works
Every pairing has to be reachable through some other category. If the candidate sets of two items, seen through a shared third category, don't overlap at all, there's no way to complete the puzzle with them paired.
Trigger
An unresolved cell where you're not sure two items can go together — check whether any item in a third category is compatible with both.
Common mistake
Only looking for direct evidence against a pairing, and missing that the absence of any connecting item is itself proof enough.
Example
If nothing that could be Mina's pet is also compatible with the red house, then Mina and the red house cannot go together, even with no clue saying so directly.
On Bambleweeny's board
Implemented in the live solver, and checked earlier in its priority order than Set Transposition — which is why Set Transposition's own harder cases turn out to already be covered by this technique.