a1 Departamento de Matemática Aplicada, E.T.S.I. Agronomos, E-28040 Madrid, Spain
a2 Department of Mathematics, University of Jyväskylä, SF-40100 Jyväskylä, Finland
Let f: A → n be Hölder continuous with exponent α, 0 < α 1, where A ⊂ m has finite m-dimensional Lebesgue measure. Then, as is easy to see and well-known, the s-dimensional Hausdorif measure HS(fA) is finite for s = m/α. Many fractal-type sets fA also have positive Hs measure. This is so for example if m = 1 and f is a natural parametrization of the Koch snow flake curve in 2. Then s = log 4/log 3 and α = log 3/log 4. In this paper we study the question of what s-dimensional sets in can intersect some image fA in a set of positive Hs measure where A ⊂ m and f: A → n is (m/s)-Hölder continuous. In Theorem 3·3 we give a general density result for such Holder surfacesfA which implies for example that Hs(E fA) = 0 for any totally disconnected self-similar set. E in this situation. In Theorem 32 we shall first show that such fA has positive s-dimensional lower density H8 almost everywhere.
(Received September 24 1992)
(Revised November 09 1992)