Dynamic Plus Region Forcing Chain

With this solving technique, we will prove the following assertions:

Because the value 1 cannot be placed elsewhere in box 1, and the results are the same, we can conclude that B8 cannot contain the value 1.

Each assertion is proved by a different chain of simple rules. The chains may be dynamic, which means that the conclusions of multiple sub-chains are combined.

Plus means that the standard Sudoku solving techniques: (Point & Claim, Naked Pairs, Hidden Pairs, and Swampfish) are applied (only when no other chain-step is found).

The details of each chain are given below. Use the view selector below the grid to switch between the graphical illustrations of the different chains.

Chain 1: If B1 contains the value 1 then B8 cannot contain the value 1 (View 1):
(1) If B1 contains the value 1 then B8 cannot contain the value 1 (the value can occur only once in the col)

Chain 2: If B3 contains the value 1 then B8 cannot contain the value 1 (View 2):
(1) If B3 contains the value 1 then B8 cannot contain the value 1 (the value can occur only once in the col)

Chain 3: If C3 contains the value 1 then B8 cannot contain the value 1 (View 3):
(1) If C3 contains the value 1 then C3 cannot contain the value 2 (the cell can contain only one value)
(2) If C3 does not contain the value 2 then B5 cannot contain the value 2 (Pointing: box 1 and col B on 2)
(3) If C3 contains the value 1 (initial assumption) then C3 cannot contain the value 4 (the cell can contain only one value)
(4) If C3 does not contain the value 4 then C2 cannot contain the value 6 (Hidden Pair: A2, C2: 4, 9 in box 1)
(5) If C3 contains the value 1 (initial assumption) then C3 cannot contain the value 6 (the cell can contain only one value)
(6) If C3 does not contain the value 6 and C2 does not contain the value 6 (4) then B5 cannot contain the value 6 (Pointing: box 1 and col B on 6)
(7) If B5 does not contain the value 6 and B5 does not contain the value 2 (2) then C5 cannot contain the value 9 (Hidden Pair: C5, F5: 2, 6 in row 5)
(8) If C3 contains the value 1 (initial assumption) then C4 cannot contain the value 1 (the value can occur only once in the col)
(9) If C4 does not contain the value 1 then A4 cannot contain the value 9 (Hidden Pair: A4, G4: 1, 8 in row 4)
(10) If A4 does not contain the value 9 and C5 does not contain the value 9 (7) then C4 must contain the value 9 (only remaining position in the box)
(11) If C4 contains the value 9 then E4 cannot contain the value 9 (the value can occur only once in the row)
(12) If E4 does not contain the value 9 then E4 must contain the value 5 (only remaining potential value in the cell)
(13) If E4 contains the value 5 then E2 cannot contain the value 5 (the value can occur only once in the col)
(14) If E2 does not contain the value 5 then H1 cannot contain the value 5 (Pointing: box 2 and row 1 on 5)
(15) If E2 does not contain the value 5 (13) then I1 cannot contain the value 5 (Pointing: box 2 and row 1 on 5)
(16) If I1 does not contain the value 5 and H1 does not contain the value 5 (14) then I2 cannot contain the value 7 (Hidden Pair: H2, I2: 5, 8 in box 3)
(17) If I1 does not contain the value 5 (15) and H1 does not contain the value 5 (14) then H2 cannot contain the value 7 (Hidden Pair: H2, I2: 5, 8 in box 3)
(18) If H2 does not contain the value 7 and I2 does not contain the value 7 (16) then G2 must contain the value 7 (only remaining position in the box)
(19) If G2 contains the value 7 then G6 cannot contain the value 7 (the value can occur only once in the col)
(20) If B5 does not contain the value 6 (6) and B5 does not contain the value 2 (2) then F5 cannot contain the value 9 (Hidden Pair: C5, F5: 2, 6 in row 5)
(21) If C5 does not contain the value 9 (7) and F5 does not contain the value 9 then D5 must contain the value 9 (only remaining position in the row)
(22) If D5 contains the value 9 then D5 cannot contain the value 4 (the cell can contain only one value)
(23) If B5 does not contain the value 6 (6) and B5 does not contain the value 2 (2) then F5 cannot contain the value 4 (Hidden Pair: C5, F5: 2, 6 in row 5)
(24) If C3 does not contain the value 4 (3) then G2 cannot contain the value 4 (Pointing: box 1 and row 2 on 4)
(25) If G2 does not contain the value 4 then H5 cannot contain the value 4 (Pointing: box 3 and col H on 4)
(26) If H5 does not contain the value 4, F5 does not contain the value 4 (23) and D5 does not contain the value 4 (22) then G5 must contain the value 4 (only remaining position in the row)
(27) If G5 contains the value 4 then G6 cannot contain the value 4 (the value can occur only once in the box)
(28) If G6 does not contain the value 4 and G6 does not contain the value 7 (19) then G6 must contain the value 8 (only remaining potential value in the cell)
(29) If G6 contains the value 8 then G4 cannot contain the value 8 (the value can occur only once in the box)
(30) If C4 does not contain the value 1 (8) then G4 cannot contain the value 7 (Hidden Pair: A4, G4: 1, 8 in row 4)
(31) If G4 does not contain the value 7 and G4 does not contain the value 8 (29) then G4 must contain the value 1 (only remaining potential value in the cell)
(32) If G4 contains the value 1 then I5 cannot contain the value 1 (the value can occur only once in the box)
(33) If C3 contains the value 1 (initial assumption) then C5 cannot contain the value 1 (the value can occur only once in the col)
(34) If G5 contains the value 4 (26) then G5 cannot contain the value 1 (the cell can contain only one value)
(35) If G4 contains the value 1 (31) then H5 cannot contain the value 1 (the value can occur only once in the box)
(36) If H5 does not contain the value 1, G5 does not contain the value 1 (34), C5 does not contain the value 1 (33) and I5 does not contain the value 1 (32) then B5 must contain the value 1 (only remaining position in the row)
(37) If B5 contains the value 1 then B8 cannot contain the value 1 (the value can occur only once in the col)