Santiago Figueira Denis R. Hirschfeldt Joseph S. Miller Keng Meng Ng André Nies Counting the changes of random Δ20 sets. 1073-1089 2015 25 J. Log. Comput. 4 https://doi.org/10.1093/logcom/exs083 db/journals/logcom/logcom25.html#FigueiraHMNN15