C1: S1,O
C1: S2,L
C1: C2,N
C2: C1,S
C2: C3,N
C2: S3,O
C2: S4,L
C3: C2,S
C3: S5,O
C3: S6,L
S1: C1,L
S2: C1,O
S3: C2,L
S4: C2,O
S5: C3,L
S6: C3,O
S6: O1,N
O1: S6,S
O1: O2,O