Bidirectional Y-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 box regardless of which configuration is correct. Because one of the two configurations must be correct, other occurrences of these values can be removed from these rows, columns or boxs.

The cycle is an Y-Cycle because only cells with two potential values are involved. Bidirectional Y-Cycles are also known as Forcing Loops or Bivalue cycles.

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}