it is commonly known as the Empty Rectangle {er} and obscurly known as a Hinge:
- Code: Select all
/ N / | . . . | . / .
N N N | . . . | . N .
/ N / | . . . | . / .
--------+-------+-------
. . . | . . . | . / .
. . . | . . . | . / .
. . . | . . . | . / .
--------+-------+-------
. . . | . . . | . / .
. X . | . . . | . N .
. . . | . . . | . / .
KEY: '/' <=> cells void of candidate 'N'
'N' <=> cells with candidate 'N'; not all are required in the box.
"-X" <=> potential eliminations of candidate 'N'
there is several way to exend the elimination of an empty rectangle here is one for example.
Grouped ER:
- Code: Select all
/ N / | . . . | / N /
N N N | x x x | N N N
/ N / | . . . | / N /
--------+-------+-------
. x . | . . . | . x .
. x . | . . . | . x .
. x . | . . . | . x .
--------+-------+-------
. x . | . . . | . x .
/ N / | / / / | / N /
. x . | . . . | . x .