Hi! Sorry, Eric, if this is a lot of work. Reject to do it, if you like, or provide only some of these. ---- Task 1 -------------- Consider I need to flatten a tree into a sum: template<int I> struct arg {}; proto::terminal<arg<1> >::type a; proto::terminal<arg<2> >::type b; proto::terminal<arg<3> >::type c; proto::terminal<arg<4> >::type d; a + b + c + d has type expr<tag::plus, arg2<a tree structure> > but I need a template function make_flat taking arbitray expressions and return expressions of type expr<sum, args4<all args in the typelist> > How can I do this in proto? ----------- Task 2: Next step: a - b + c should first be transformed into a + (-b) + c and then transformed into the sum. Could you please provide full compilable examples? ------ Task 3: Next step: I want to detect simultaneous occurences of x and -x and have them dropped from the typelist of my sum. Please provide an example that detects this for terminals only, then one which also works for (a*b - a*b) and returns expr<tag::nil, nulllist> (BTW, is there a nil/null tag in proto?) --------- Task 4: Write an expand function that for a*(b+c) returns a type representation a*b+a*c ----- Markus