Five friends, Purva, Roshan, Vibhor, Luna and Anuj, are wearing five different coloured T-shirts, red, black, purple, yellow and blue. Each of the friends is allergic to one of the following: nuts, dairy, cats, fish and dust, such that no two has the same allergy. Luna is allergic to cats but is not wearing a purple T-shirt. The one wearing a yellow T-shirt has dust allergy. Purva is wearing a black t-shirt but is not allergic to dairy or fish. Vibhor is wearing a purple T-shirt but does not have fish allergy. Luna is wearing a blue T-shirt. Roshan is wearing a red T-shirt. Who is allergic to dust?