The Stack in ALG Mode

[Powa]

According to Appendix B, the stack in ALG mode holds the last 4 results. That's fine. It also says:

"Note that once a two-numbered function (such as +, -, x, / or y^x) has has the second argument entered, the two arguments cannot then be swapped using x><y because when the second argument is entered it replaces the first,..."

Where is the first argument stored then?

In RPN mode the y^x makes sense, you key in a value which goes into x register and when you key in the second value, it goes into the y register with the new value being in the x register. So the key makes logical sense in RPN mode. But I don't know what logic to use for ALG mode.