Naked Subset :

A unit constraint where N cells have candidates for only the same N digits. All of the same candidates can be eliminated from all common units.

Naked Single :

A unit constraint where a single cell has only a single candidate.

Notes :

This strategy can, in some cases, be performed without the use of pencilmarks. Counting one through nine of known digits in all common units will displace the single unknown digit.

"When you have eliminated the impossible, whatever remains, however improbable, must be the truth." -- Sherlock Holmes

Naked Pairs :

A unit constraint where 2 cells have candidates for only the same 2 digits.

Naked Triples :

A unit constraint where 3 cells have candidates for only the same 3 digits.

Naked Quads :

A unit constraint where 4 cells have candidates for only the same 4 digits.

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Hidden Subset :

A constraint in at least one common unit where candidates for N digits occur in N cells. All of the other candidates can be eliminated from those cells.

Hidden Single :

A constraint in at least one common unit where a candidate for a single digit occurs once.

Notes :

Elimination-wise, this strategy, after the constraints of the Hidden Subset strategy have been applied, also eliminates candidates with the constraints of the Naked Single strategy.

The reason the Naked Single strategy is applied when using this strategy is NOT because they are combined, but because of cause and effect usage of this strategy -- the effect of the Hidden Single Strategy causes the Naked Single Strategy to be applied on the same common units.

Hidden Pairs :

A constraint in at least one common unit where candidates for 2 digits occur in 2 cells.

Hidden Triples :

A constraint in at least one common unit where candidates for 3 digits occur in 3 cells.

Hidden Quads :

A constraint in at least one common unit where candidates for 4 digits occur in 4 cells.

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Locked Candidates :

A constraint in a box and non-box unit where candidates for a single digit occur in just one of those units, and the intersection. All occurrences of that digit outside of the intersection can be removed from common units.

Note:

There are two types of Locked Candidates -- Pointing and Box-line. They are determined by which unit, excluding the intersection, that the possible candidates are in.

Pointing Single :

A constraint in a box and non-box unit where candidates for a single digit occur only in the non-box unit -- one candidate of which must only be in the intersection.

Note:

Although similar to the Hidden Single strategy, this strategy's sole purpose is for the elimination of candidates, not placement of candidates.

Pointing Pairs :

A constraint in a box and non-box unit where candidates for a single digit occur only in the non-box unit -- two candidates of which must only be in the intersection.

Pointing Triples :

A constraint in a box and non-box unit where candidates for a single digit occur only in the non-box unit -- three candidates of which must only be in the intersection.

Box-Line Reduction :

A constraint in a box and non-box unit where candidates for a single digit occur only in the box unit -- at least one candidate of which must only be in the intersection.

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Fish Subset :

A constraint in N distinct units of the same type where N candidates for a single digit lie only on N units of another type. All other occurrences of that candidate can be removed from the latter units.

Needle-Fish :

A constraint in 1 distinct unit of the same type where 1 candidate for a single digit lie only on 1 units of another type.

X-Wing :

A constraint in 2 distinct units of the same type where 2 candidates for a single digit lie only on 2 units of another type.

Notes:

The classic X-Wing occurs when 2 of the same non-box units have candidates only in 2 different non-box units of the other type.

The same effect of Pointing Pairs occurs when 2 box units have candidates in 2 of the same non-box units.

The same effect of a Line-Box Reduction occurs when 2 of the same non-box units have candidates in only 2 boxes

Sword-Fish :

A constraint in 3 distinct units of the same type where 3 candidates for a single digit lie only on 3 units of another type.

Jelly-Fish :

A constraint in 4 distinct units of the same type where 4 candidates for a single digit lie only on 4 units of another type.

Squirmbag :

A constraint in 5 distinct units of the same type where 5 candidates for a single digit lie only on 5 units of another type.

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