緩成長階層
g 0 ( n ) = 0 {\displaystyle g_{0}(n)=0}
g α + 1 ( n ) = g α ( n ) + 1 {\displaystyle g_{\alpha +1}(n)=g_{\alpha }(n)+1}
g α ( n ) = g α [ n ] ( n ) {\displaystyle g_{\alpha }(n)=g_{\alpha [n]}(n)} ( α {\displaystyle \alpha } が極限順序数のとき、 α [ n ] {\displaystyle \alpha [n]} は α {\displaystyle \alpha } の n {\displaystyle n} 番目の順序数)