where \(\Xi\)(n) is the xi function, which was used due to Adam Goucher's mistaken claim that it outgrew Rayo's function. The function is a naive extension of the xi function and is easily beaten by functions such as the Rayo/FOST function and its stronger cousin the FOOT function He later upgraded the function, adding the rules: * \( ext{Arx}(a,b,c,\cdots,y,1) = ext{Arx}(a,b,c,\cdots,y)\) * \( ext{Arx}(a,b,c,\cdots,x,y,z)\) \(= ext{Arx}( ext{Arx}(a,b,c,\cdots,x,y,z-1),\cdots, ext{Arx}(a,b,c,\cdots,x,y,z-1),1)\)