  What Ajdukiewicz showed in his 1935 paper was that we can develop a calculus of grammatical combination using such a notation: we take a putatively well-formed expression, rearrange it if necessary into functor-first order, then see if we can “multiply out” arguments and functors to arrive at a single categorial index. If we can, the complex expression is grammatical, well-formed, or syntactically connected. For example ‘\(\isa\{Aa\}\)’ is syntactically connected as follows: writing the category of an expression \(e\) as \(|e|\) we have