area1           area2        area3
            BFR1a BFR1b  BFR2a BFR2b   BFR3a BFR3b
              |  \         /    \        /  |
              ................................
              .                Core          .
              ................................
              |    /       \    /        \  |
            BFR4a BFR4b  BFR5a BFR5b   BFR6a BFR6b
             area4          area5        area6