Questions on the current stage of concepts

[MisterDrgn]

Thanks for the suggestion. I tried this out, and although it works, AddableColl 
appears to end up being identical to Coll, rather than incorporating the 
additional "Addable" constraint. For example, it allows you to calls @["0", 
"1", "2"].sum, and you only get the error inside the function when it tries to 
add values.