“…While the Hausdor¤ measure of non-compactness is established to study modulus of noncompact convexity which is important in the geometry of Banach and Hilbert spaces it is also used to …nd necessary and su¢ cient conditions for a matrix operator on a given sequence space to be a compact operator (see [24,25,32]). Topological properties of certain sets of sequence spaces are investigated in the papers [1-3, 7-10, 13, 16, 21-23, 31, 33, 34] and [40].…”