The three Almost Locked Sets: ALS A: box 9: H7, I8, G9 and H9 {2, 3, 7, 8 and 9} ALS B: col H: H5, H7 and H9 {2, 3, 8 and 9} ALS C: row 9: C9 and D9 {1, 7 and 9} share the common values x, y and z such that: z- A -x- C -y- B -z which means: ALSs A and C share the restricted common (RC) value x = 7, ALSs C and B share the restricted common (RC) value y = 9, ALSs A and B share the unrestricted common value/s z = 2 and 3Therefore G7-3, H3-2 can be removed.
The logic is: if z is not in ALS A, then ALS A contains x because only one digit may miss from an ALS. That means that ALS C must contain y (x is missing from C) and thus ALS B must contain z (y is missing from B). The other way round works as well: If ALS B does not contain z then ALS A must. Hence z can be removed from all other cells which see all z's in both ALS A and ALS B.
Note that x and y may not be the same digit.
The restriction in Restricted Common Candidate is that all instances of the
value in both ALSs must be siblings (ie all "see" each other).
Note that an ALS-XY-Wing is an ALS-Chain of length 3. ALS-XY-Wing's are handled separately because in ALS-Chain only RC's may not appear in the overlap (common cells) of the two ALSs, if any.