The non-compactness of square

This note proves two theorems. The first is that it is consistent to have for every n , but not have . This is done by carefully collapsing a supercompact cardinal and adding square sequences to each ω n . The crux of the proof is that in the resulting model every stationary subset of ℵ ω +1 ⋂ cof( ω ) reflects to an ordinal of cofinality ω 1 , that is to say it has stationary intersection with such an ordinal. This result contrasts with compactness properties of square shown in [3]. In that paper it is shown that if one has square at every ω n , then there is a square type sequence on the points of cofinality ω k , k > 1 in ℵ ω +1 . In particular at points of cofinality greater than ω 1 there is a strongly non-reflecting stationary set of points of countable cofinality. The second result answers a question of Džamonja, by showing that there can be no squarelike sequence above a supercompact cardinal, where “squarelike” means that one replaces the requirement that the cofinal sets be closed and unbounded by the requirement that they be stationary at all points of uncountable cofinality.