premise: Charles has only visited Mauritania, Carl has only visited Vietnam, Nathaniel has only visited Pakistan, Marvin has only visited Saint Vincent & the Grenadines, Sidney has only visited Central African Republic, Tyrone has only visited Haiti, Tim has only visited Guyana, Jerome has only visited Côte D'ivore, Ricky has only visited Kyrgyzstan, Raymond has only visited Grenada, Daniel has only visited Botswana
hypothesis: Carl didn't visit Singapore