Adam and his wife Betty, Charles and his wife Diane, and Emilio and his wife Felicity problem:
ACEF|---->BD>----|
ACEF|----<B<----|D
ACE|---->BF>----|D
ACE|----<B<----|DF
AB|---->CE>----|DF
AB|----<EF<----|CD
BF|---->AE>----|CD
BF|----<D<----|ACE
B|---->DF>----|ACE
B|----<A<----|CDEF...