Floating prepositions (or stranded prepositions) are a well-documented syntactic phenomenon in English and other natural languages where a preposition appears separated from its complement (e.g., 'What are you looking at?'). No citation is needed for this basic linguistic fact.
The claim asserts that floating prepositions exist in natural language. This is a basic, trivially true descriptive fact of syntax and everyday observation (comparable to saying nouns or verbs exist). Therefore, following STEP 0, this is classified as COMMON_KNOWLEDGE, requiring no citations or paper matching.