Concatenative Combinators aren’t a #concatenativelanguage in the strict sense. Although it’s true that any two valid programs catenated together form a valid program, it is not true that any bisection of a program results in two valid programs. This is because concatenative combinators includes quotations, which makes it a Dyck Language. The correct rules are that 1. Inserting any valid program into another valid program results in a valid program. This includes inserting at the end or the beginning, which are also catenation. 2. Removing any valid program from a valid program leaves a valid program. That includes removing from the end or the beginning. 3. Valid programs contain balanced quotes. https://tunes.org/~iepos/joy.html