; a generic 4-membered ring
SSTR S1 A (2 3) (0 1 2)
SSTR S2 A (2 3) (0 1 2)
SSTR S3 A (2 3) (0 1 2)
SSTR S4 A (2 3) (0 1 2)
LINK S1 S2
LINK S2 S3
LINK S3 S4
LINK S1 S4
