default constructor

[MattJean]

In some cases it would be interesting to have default constructors for the tci (1-2 and trees).

Thanks

[yurielnf]

I omitted it to make one thinks before using this two-stage initialization. Are you sure you need it? Here they explain why:
https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#Rc-complete