1. Homotopy Invariant Algebraic Structures on Topological Spaces;Boardman,1973
2. Homotopy Limits, Completions and Localizations;Bousfield,1972
3. Tensor product of operads and iterated loop spaces;Dunn;J. Pure Appl. Algebra,1988
4. G. Dunn, Uniqueness of n-fold delooping machines, to appear.