What does $\log^3$ stand for in this paper by K. Győry?

79 Views Asked by At

In this paper from 1980 K. Győry proved an upper bound for the absolute value of the solutions to a given Thue-Mahler equation, but I don't understand what he meant with $\log^3$.

Namely, consider a number field $L$ of degree $\ell \geq 1$. In Corollary 1, page 5, he gives bounds for the solutions of a bivariate Thue-Mahler equation $$ f(x,y) = \beta \pi_1^{z_1} \dotsb \pi_s^{z_s} \quad \text{in } x,y \in \mathcal{O}_L \text{ s.t. } N((x,y)) \leq d \text{ and } z_1,\dotsc,z_s \in \Bbb{Z}_{\geq 0} \tag{1} \label{eq:1} $$ with $d \geq 1$ a rational integer, $\beta,\pi_1,\dotsc,\pi_s$ non-zero algebraic integers in $L$ where $\pi_1,\dotsc,\pi_s$ are non-units such that $(\pi_i)$ are powers of prime ideals, and $f(X,Y) \in \mathcal{O}_L[X,Y]$ such that:

  • $\deg f \geq 3$,
  • $f(1,0) \neq 0$, and
  • $f(X,1)$ has at least three distinct roots.

Those bounds are defined (multiplicatively) in terms of the constant $$ T^* = \exp\left(c_{f,\beta,\pi_1,\dotsc,\pi_s} (\log P)^5 \log^3(R_G^* h_G)\right) $$ where:

  • $P \geq \max\operatorname{rad}(N(\pi_i)) \geq 2$,
  • $c_{f,\beta,\pi_1,\dotsc,\pi_s}>0$ is a constant depending on $c_{f,\beta,\pi_1,\dotsc,\pi_s}$,
  • $h_G$ is the class number of the splitting field $G$ of $f$, and
  • $R_G^* = \max(R_G, e)$, with $R_G$ the regulator of $G$.

Here's my problem: Since both $(\log P)^5$ and $\log^3(R_G^* h_G)$ appear in the same formula, I assume that $$ \log^3(R_G^* h_G) \neq \log(R_G^* h_G) \log(R_G^* h_G) \log(R_G^* h_G) $$ which, as far as I know, leaves only $$ \log^3(R_G^* h_G) = \log\log\log(R_G^* h_G). $$ But consider for example $L = \Bbb{Q}$, $f = X^4 - Y^4$, $\beta = 1$, $\pi_1 = 2$, and $\pi_2 = 5$. Then $f(X,1)$ has $4$ distinct roots over its splitting field $G = \Bbb{Q}[i]$ so, as far as I understand, we are in the hypotheses of Corollary 1. However, G has regulator $R_G = 1$ and class number $h_G = 1$, so $\log\log\log(R_G^* h_G) = \log\log\log(e)$ isn't defined. Furthermore, even interpreting $$ \log\log\log(e) = -\infty $$ (over the extended reals) doesn't lead me anywhere: then $T^* = 0$ would give the upper bound $$ 2^{z_1} \cdot 5^{z_2} \leq 0 $$ for every solution $(x,y,z_1,z_2)$ of $\eqref{eq:1}$, i.e. that the equation doesn't have any solution. But this isn't the case, because $$ 3^4 - 1^4 = 80 = 2^4 \cdot 5. $$