U[0] = 2 ([n] is called a "Dimension")
U[n] = U[n-1]{U[n-1]}U[n-1]
U[0][0] = U[2]
U[n][0] = U[n-1][U[n]]
U[n][m] = U[U[n,m-1]]
U[n][0][0] = U[U[n],U[n]]
U[n][m][0] = U[n][m-1][U[n,m]]
U[n][m][l] = U[U[n,m,l-1]][U[n,m,l-1]]
U![0][0] = U[U!][U!][U!]... where ! is the rest and [U!] is repeated #!+1 times, #! is the amount of dimensions in !
U![n] = U[U![n-1]][U![n-1]][U![n-1]][U![n-1]]... where [U![n-1]]'s is repeated #! times