Using existential quantifier within implication
Your statement attempts to be express in formal logic the following sentence:


  There exist $\sigma_{opt}$ and $n$ in $R^+$ such that if $0 &lt; n &lt; 1$ then $\sigma_{opt} = n$.


The attempt at translation goes about by replacing English words by mathematical symbols, while keeping English syntax. Unfortunately, that is not how this sort of translation works. Just as when translating between human languages the syntax needs to be changed, here as well you have to conform to the syntax of statements in predicate logic. Your statement is, unfortunately, ungrammatical (more formally, it is not well-formed, that is, it is not a wff).

The syntax of sentences in predicate logic is described in many sources, so let me just mention that the following sentence is valid:
$$
\exists \sigma_{opt} \in R^+ \exists n \in R^+ \; (0 &lt; n \land n &lt; 1) \to \sigma_{opt} = n.
$$
We often allow shortcuts to be used, and so consider the following statement to be valid as well (standing for the former statement):
$$
\exists \sigma_{opt},n \in R^+ \; 0 &lt; n &lt; 1 \to \sigma_{opt} = n.
$$
You are using a different shortcut for folding the two existential quantifiers, but your convention is not standard; it's better to use standard conventions, unless there's a good reason to deviate from standard practice.

Finally, I'm not sure what your statement is supposed to express, but it probably doesn't express what you were hoping for: it doesn't depend on any parameter (this is why it's a statement rather than just a formula), which was probably not your original intention.