How Pair ends works

Pair ends gives the other animal to an empty tile at either end of two matching animals side by side. It follows from Three's a crowd, one of Pawmoku's two rules. In the first 45 library puzzles it decides 720 tiles, in 45 of the boards. Its earliest use there is step 1 of 4x4 puzzle 1.

Why it works

Before: empty, cat, cat, empty, empty, empty.

After: dog, cat, cat, dog, empty, empty.

A cat at either end of the two cats would make three cats in a row. Both empty ends must be dogs.

When to look for it

Look beside pairs in every row and column. A pair at the edge has only one neighbouring tile inside the line.

Three line examples

Example 1

Before: dog, dog, empty, empty, empty, empty.

After: dog, dog, cat, empty, empty, empty.

Example 2

Before: empty, empty, cat, cat, empty, empty.

After: empty, dog, cat, cat, dog, empty.

Example 3

Before: empty, dog, dog, empty, empty, empty, empty, empty.

After: cat, dog, dog, cat, empty, empty, empty, empty.

Find it in practice

4x4 Puzzle 1: Pair ends first decides a tile at step 1.
6x6 Puzzle 1: Pair ends first decides a tile at step 1.
8x8 Puzzle 1: Pair ends first decides a tile at step 1.