Hello, Thanks for reply. However, the second method of extending a range: http://www.boost.org/doc/libs/1_55_0/libs/range/doc/html/range/reference/ext... states that specializing both metafunctions is necessary. In particular this: https://gist.github.com/Kojirion/9714131 fails to compile. It will compile - and produce correct result - by commenting out all lines (ie defining a mutable iterator, which really isn't...) Albert