The starting point is a repeat of the definition posted in < July 2012 >as the subject of (welcome) critique.

Denis (and possibly Blue) may I suggest that you re-post your queries and observations here for me to respond to.

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Junior Exocet Definition

An Exocet exists when it can be shown that a base cell pair and two target cells must reduce to holding the same two digits out of a set of 3 or 4 base cell candidates. This then allows any non-base candidates to be eliminated from the target cells.

As defined by champagne, the way this base-target cell equivalence is demonstrated is unrestricted and may for example use multiple templates. However analysis has shown that in most cases there are identifiable pattern elements that exist.

The Junior Exocet (JE) pattern restricts the base and target cells to a single band of boxes and the digits to those in the base cells.

The Junior Exocet Plus (JE+) extends this by also checking for other candidates that are locked in the cells of interest.

Pattern Element Map

- Code: Select all
`*-------*-------*-------*`

| B B . | . . . | . . . | B = Base Cells

| . . . | Q . . | R . . |

| . . . | Q . . | R . . | Q = 1st Object Pair

*-------*-------*-------* R = 2nd Object Pair

| . . S | S . . | S . . |

| . . S | S . . | S . . | S = Cross-line Cells

| . . S | S . . | S . . |

*-------*-------*-------* . = Any candidates

| . . S | S . . | S . . |

| . . S | S . . | S . . |

| . . S | S . . | S . . |

*-------*-------*-------*

The different cell pairs occur in different boxes in the same band (the JE band).

In each object pair one cell will be a target cell and the other will be a companion cell that will reduce to a non-base candidate.

The three cross-lines intersect this band as shown, passing through the object cell pairs but not the base cell pair.

Requirements

1) The base cells must be restricted to a set of three or four digits (the base candidates)

2) Each object cell pair must only be capable of accommodating one base digit. This requires that they

a) have one cell that contains at least one base candidate (the target cell) and the other that contains none of them (the companion cell)

or

b) (JE+) must overlap an Almost Hidden Set that restricts the object cells to holding one base digit.

The simplest and most frequent situation will be when the AHS is an Almost Hidden Pair with a single extra digit locked in the object cells.

3) The two target cells must be forced to reduce to different base digits. This is satisfied when all occurrences of a digit (solved or not) in the "S", cross-line, cells are contained by two houses. A way to check this is to consider how many lines would be needed to cover all of them.

These diagrams show examples of the maximum number of occurrences of a digit in the "S" cells that can be contained by different combinations of two houses.

- Code: Select all
`v v v`

r4 . . \ | \ . . | \ . . . . O | \ . . | O . . . . \ | \ . . | O . .

r5 . . O | O . . | O . . < . . O | \ . . | O . . . . O | O . . | O . . <

r6 . . \ | \ . . | \ . . . . O | \ . . | O . . . . \ | \ . . | O . .

r7 . . \ | \ . . | \ . . . . O | \ . . | O . . . . \ | \ . . | O . .

r8 . . O | O . . | O . . < . . O | \ . . | O . . . . \ | \ . . | O . .

r9 . . \ | \ . . | \ . . . . O | \ . . | O . . . . \ | \ . . | O . .

2 Parallel Lines(I) 2 Parallel Lines(II) 2 Orthogonal Lines

rows 5 & 8 columns 3 & 7 row 5 & column 7

Eliminations

In JE patterns any non-base candidates can be eliminated from the target cells

In JE+ patterns (relying on condition 2b) the identity of the target cell won't be known. One object cell must eventually hold a base digit, and the other a candidate locked in the AHS, so any candidates that aren't in either set can be eliminated from both the object cells.

After a JE has been found

When the givens in the JE band are suitably placed, the inference that the two target cells must contain different base digits will often allow eliminations to be made in the target cell mini-lines.

When a base digit is known it will often form one of two Swordfish patterns and it will be possible to eliminate it from the fin cells common to both.

Short Proof

The columns of interest are c347 in the pattern map.

In the JE band the digits that are true in the base cells will be excluded from c3r123, c4r1 and c7r1.

From condition 2, the objects cells are limited to holding 2 truths at most for this digit pair. With no other openings in the JE band there therefore must be at least 4 truths in the 'S' cells to satisfy the three columns.

But condition 3 limits the number of truths that can be held in these cells to 4 at most, (2 for each digit).

Consequently each digit must be true twice in the 'S' cells and once in the object cells.

Additional Available from JE Patterns

Once a JE pattern has been found, additional follow-on inferences may also be available as listed here: < Additional JE Inferences >.

[edit] Link to additional inferences added.