finished tour50

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
fixes comment of tour50

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
finished tour51

Signed-off-by: Kouhei Maeda <mkouhei@palmtb.net>
finished tour52

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