The {7} cells
The {8} cells {1} are an Almost Locked Set (ALS) that is double-linked to the bivalue cell {2} through both values {4} and {3} to create a ring/loop. Regardless of the value of {2}, the double-link forces the {8} ALS cells to have a different value to {2}, so these {7} values are "locked into" these {7} cells, ergo it's a Locked Set. Hence all of the Rings values can be removed from other cells which see all occurrences of that value in the Ring.
Therefore