I need some help with the development of an expression, it is: $$\delta\left\{\frac{\partial^3F(q^1,q^2,t)}{\partial t\partial q^1 \partial q^2}\right\}$$
with each of $q^1,q^2$ are functions of $t$. I want to know this is expression is equal to...
In the other hand, can the variational $\delta$ operator conmute with the derivate ($d/dt$) and partial derivate ($\partial/\partial t$) operators?. I'm a newbie, please don't be rude... Thanks in advance...
Any book to search for?