A minimax argument to a stronger version of the Jacobian conjecture

The main result of this paper is to prove the strong real Jacobian conjecture under the symmetric assumption and reveals the link between it and the Jacobian conjecture. Precisely, we assume that $F: \mathbb{R}^n \to \mathbb{R}^n$ is of $C^1$ map, $n\geqslant 2$, if for some $\varepsilon >0$, $0\notin Spec(F)~~\mbox{and}~ Spec(F+F^T) \subseteq (-\infty,-\varepsilon)~\mbox{or} ~(\varepsilon,+\infty),$ where $Spec (F)$ denotes all eigenvalues of $JF$ and $Spec (F+F^T)$ denotes all eigenvalues of $JF+JF^T$, then we show that $F$ is injective. It is proved by using a minimax argument.