This is false. RPN lends itself perfectly fine to n-ary operations. For instance for a 3-ary function:RPN only really lends itself to 1- or 2-value functions:
Luckily you don't need universal agreement, just a specification. For instance on HP's calculator's they usually use x to represent the top-most argument on the stack, and y the next so.Therefore, it would be difficult to implement in RPN (or any other system) with universal agreement.
HP developed the RPL (Reverse-Polish LISP) programming language for their calculators which standardize the functions I mentioned earlier. It also includes syntax for actually working with complex functions and even defining your own. You're right that there is no universal standard though, just as 5 3 ^ could mean both 5^3 or 3^5 since there is no universally agreed upon way of ordering it.Agreed, but to my knowledge there hasn't been any standardization for such expressions.
I completely agree, but keep in mind that many calculator producers have taken the trouble to standardize the order. Due to the fact that when writing definite integrals ([itex]\int_a^b f(x)dx[/itex]) we write the arguments in the order a b f so the natural candidate is A B F INTEGRATE, but F A B INTEGRATE is also imaginable even though I have never seen that order. Keep in mind however that this problem is in no way exclusive to RPN calculators/languages. Most calculators and programming languages don't have an integral sign as such either so you end up writing INTEGRATE(a,b,f) which also relies on some ordering.Besides, you could just as easily say "take the integral of function F from a to b" as "take the integral from a to b of function F"
To us, they mean the same thing, but a calculator, needs to have strict rules. Once there is standardization in the order in which the variables are entered, then no, there is no confusion, but unless and until that happens, it is not necessarily clear.