The notation $L^\alpha_{\beta,\gamma}$ refers to the set of sentences of predicate calculus with less than $\alpha$ variables, conjunctions of size less than $\beta$, and quantification over families of less than $\gamma$ variables.  Formally (and assuming I was not [mistaken][1]) the following are formulas of $L^\alpha_{\beta,\gamma}$ in addition to the atomic formulas:

* $\neg\phi$ if $\phi\in L^\alpha_{\beta,\gamma}$
* $\underset{i\in I}\bigvee \Phi_i$ if $|I|<\beta$ and $(\forall i\in I)\Phi_i\in  L^\alpha_{\beta,\gamma}$ and $|FV(\underset{i\in I}\bigvee \Phi_i)|<\alpha$
* $(\exists \{x_i\}_{i\in I})\phi$ if $|I|<\gamma$ and $\phi\in L^\alpha_{\beta,\gamma}$

So, my question is: why $\gamma$?  More specifically, when is $L^\alpha_{\beta,\gamma}\neq  L^{min(\alpha,\gamma)}_{\beta,\infty}$?

I think they are the same, but if that is the case I can't see why the notation hasn't been reduced to simply $L^\alpha_\beta$.  My reasoning goes like this: 

* If $\alpha < \gamma$ no quantifier can actually quantify over $\alpha$ or more  variables (unless some don't appear, in which case you can just delete them), since any formula which did so would involve a subformula with $\alpha$ or more free variables, which would be ill-formed..
* If $0 < \gamma < \alpha \leq \omega$ you can just nest finitely many $<\gamma$-variable quantifiers to achieve $<\alpha$-variable quantification, so increasing $\gamma$ to be equal to $\alpha$ will admit additional well-formed formulas, but each of them will be equivalent to some formula which had already been admitted.
* If $\gamma < \alpha$ and $\omega < \alpha$ then a formula with $\gamma$ or more free variables can never appear as a subformula of a closed formula (sentence) because no cardinal $<\gamma$ multiplied by a finite cardinal (nesting depth) is ever equal to a greater cardinal.  So reducing $\alpha$ to equal $\gamma$ would not change the set of well-formed sentences (although I guess it might affect the set of formulas, but the sentences are what really matter, right?)

  [1]: http://mathoverflow.net/questions/25071/bounded-variable-logic-less-than-alpha-variables-equivalent-to-every-subfo