Double Junior Exocet

A Double Junior Exocet (Double JE) is what you get when two Junior Exocet patterns share the same base digits. The pairing produces extra deductions that neither JE finds in isolation — typically the deepest move available short of forcing chains.

Read the Junior Exocet page first if you haven't yet. This page assumes you know the JE vocabulary.

What "double" means

Two JEs are paired into a Double when:

• They carry the same set of base digits (three or four digits common to both base pairs).
• They sit on the grid without overlapping their base or target cells.
• Their cross-line structure is compatible — i.e. the rows or columns their S-cells live in are aligned in a way that lets the combined deduction below fire.

Some treatments also accept pairs of JEs with overlapping but not identical base digit sets. The app implements the strict same-base form, which is the original and most common formulation. Wider notions exist but the boundary is debated and outside the app's detection scope.

What you can eliminate

A Double JE adds two rules on top of each JE's own catalogue:

• Rule 1. A base digit is false in every cell that sees all four target cells, or all four base cells. This generalises JE's Rule 10 to the union.
• Rule 2. Treating the union of the two JEs' S-cells as one big S-set, every base digit must still occupy at most two cover houses across that union. Non-S cells in those cover houses cannot carry the digit. This generalises JE's Rule 11 and is structurally identical to Swordfish logic on the combined S-set.

Both rules can produce eliminations on cells far away from either JE individually, which is what makes the Double form disproportionately powerful.

How common is it really?

Among curated "hardest puzzle" collections, the Double form shows up in a meaningful fraction of the entries — often cited as a few thousand puzzles per ~30 000 candidate-hard ones. Treat that as suggestive rather than load-bearing: those collections are themselves curated for hardness, so they over-represent the pattern compared to ordinary play. In typical puzzles Double JE is still rare — but as a share of the puzzles where any Exocet fires, the Double form dominates.

How to spot one by hand

If the app has already shown you a JE elsewhere on the board, the fastest way to find a Double is:

1. Note the JE's base digits.
2. Scan the other two bands for a second JE with the same base digits.
3. If you find one, check that the two JEs use distinct base and target cells.
4. Combine their S-cells into one set. For each base digit, see if it still fits in two rows or two columns across that combined set.
5. If yes, you have a Double JE — apply Rule 1 to cells seeing all four targets (or all four bases), and Rule 2 to non-S cells of the cover houses.

Looking for Double JEs from scratch (no JE in hand) is the same mini-line scan as a single JE, repeated across all three bands.

Related techniques

• Junior Exocet — The single pattern this technique is built on.
• Almost Locked Sets — Another "structural template" technique.
• Death Blossom — Another extreme-difficulty exotic.