MeowSolverDouble-cat strategy · step 2 of 4
The pair squeeze
Every row, column, and color owes two cats, and cats can’t touch — so a pair can never clump. A square that touches all of its unit’s other open squares has no room left for a partner, and dies on the spot.
Green’s open squares form a plus sign. The center touches all four arms — a cat there leaves green nowhere untouched for its second cat. Cross the center now.
Run the check on any color that still needs both cats: pick one of its open squares and ask, does this square touch every other one? If yes, it can never hold a cat — because the partner would have to sit in a square the first cat touches. In the example the four arms are fine (top and bottom arm are two apart, a legal pair), but the center is doomed either way.
This is the deduction you will use most in double-cat play. Small colors, colors chewed up by earlier crosses, and rows or columns reduced to a tight cluster all trip over it constantly — on the real double duck boards we tuned against, the pair squeeze fired more often than any other technique.
The squeeze from outside
Purple is down to three open squares. The highlighted gold square touches two of them at once — a cat there would leave purple a single square for a pair. Cross it, even though it isn’t purple.
The squeeze also works from outside the unit. A cat doesn’t have to belong to a color to strangle it: if placing a cat somewhere would leave a two-cat color without two open squares that don’t touch each other, that placement is impossible. In the example purple’s three survivors run down a diagonal; only the top and bottom of that chain sit far enough apart to form a legal pair — and the highlighted square touches exactly those two, leaving the middle square alone. One survivor is not a pair.
The habit: whenever a color drops to three or four open squares, glance at the squares hugging that cluster from outside. Several of them are usually free crosses.
MeowSolver shows both forms as a Pair squeeze hint — it outlines the squeezed unit’s open squares and marks the square that would leave no room for the pair.