finished tour24, but I don't understand this

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
finished tour25

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
finished tour26

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
finished tour27

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
finished tour28

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
finished tour29

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
finished tour30

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>