 – which cannot be define over \(\textsf{FO}(\texttt{LFP})\) without using \(\leq\). More generally, the question of there exists a logic which captures  \( \textbf{P}\) over unordered structures is currently one of the major open questions in descriptive complexity.  See, e.g., (Ebbinghaus and Flum 1999) and (Chen and Flum 2010).