Bidirectional Cycle
The cells {0} form a bidirectional cycle: there are exactly two ways
of placing the values in these cells, forming two different possible
configurations. Some values appear in a row, column or block regardless of the
chosen configuration. Because one of the two configurations must be correct, other
occurances of these values can be removed from these rows, columns or blocks.
The two configurations of the bidirectional cycle are enforced by two complementary,
circular chains of implications. The details of each chain are given below.
Cycle details, forward direction (View 1):
{3}
Cycle details, reverse direction (View 2):
{4}