Daniel Dennett noted that it is possible that such indeterminacy problems remain only hypothetical without them occurring in reality. Dennett constructs a "Quinian crossword puzzle" that is 4x4 and the words that are to be written in the crossword puzzle must satisfy both the across and down definitions. Since there are multiple constraints on this crossword puzzle there is one solution. Thus we can think of the brain and its relation to the external world as a very large crossword puzzle that must satisfy exceedingly many constraints to which there is only one possible solution. Therefore, in reality we may end up with only one physical isomorphism between the brain and the external world.