Toward a Weakly Invariant Complexity Theory - Walter A. Burkhard; F. W. Kroon (SWAT, 1971)

On a complexity-based way of constructivizing the recursive functions. - F. W. Kroon; Walter A. Burkhard (Stud Logica, 1990)

The intrinsic difficulty of recursive functions. - F. W. Kroon (Stud Logica, 1996)