Unary X-Chain

If we assume that G5 does not contain the value 8, it follows (through a Forcing X-Chain) that G5 must contain the value 8. Therefore we can conclude that G5 contains the value 8.

Unary Chains start with a simple assumption that a cell is/not one of its potential values, which is proven to be either true or false.

X-Chaining means that:
(1) when a cell is assumed to be a value then other possible positions for this value in this cells three region are removed
(2) when a cell is assumed to not be one of its potential values and there are only two positions for this value in one of this cells three regions then the other cell must be this value.

The forcing chain consists of a chain of implications based on simple rules. The chain is an X-Chain, because it only involves a single value. The details of the Forcing Chain are given below.

Note that Unary X Chains which contain 6 cells are also known as Turbot Fish.

Details of the Forcing Chain:
(1) If G5 does not contain the value 8 then I5 must contain the value 8 (only remaining position in the box)
(2) If I5 contains the value 8 then I7 cannot contain the value 8 (the value can occur only once in the col)
(3) If I7 does not contain the value 8 then C7 must contain the value 8 (only remaining position in the row)
(4) If C7 contains the value 8 then C1 cannot contain the value 8 (the value can occur only once in the col)
(5) If C1 does not contain the value 8 then B1 must contain the value 8 (only remaining position in the box)
(6) If B1 contains the value 8 then B6 cannot contain the value 8 (the value can occur only once in the col)
(7) If B6 does not contain the value 8 then A4 must contain the value 8 (only remaining position in the box)
(8) If A4 contains the value 8 then E4 cannot contain the value 8 (the value can occur only once in the row)
(9) If E4 does not contain the value 8 then E9 must contain the value 8 (only remaining position in the column)
(10) If E9 contains the value 8 then G9 cannot contain the value 8 (the value can occur only once in the row)
(11) If G9 does not contain the value 8 then G5 must contain the value 8 (only remaining position in the column)