The museum' s night security guard maintains that the thieves who stole the portrait did not enter the museum at any point at or above ground level
Ttherefore, the thieves must have gained access to the museum from below ground level
The store's competitors claim that the store, in selling off the shirts at those prices, neither made any profit nor broke even. Consequently, the store's customers must have been able to buy shirts there at less than the store's cost.