Decidec = \(f_{10\uparrow^{10}10}(10\uparrow^{10\uparrow^{10}10}10)\) where \(f_m(n)\) is the fast growing hierarchy but \(f_0(n) = n\rightarrow_{10}n\) (too bad I don't have MathJax here, so I will just type the format out and hope someone will understand.)