Is there a RPN operation that does nothing? (NOP)

[Thomas Okken]

(01-04-2018 02:44 AM)tcab Wrote:  What is the best RPN command (for say, 42s/free42) that does nothing?

Everything has the side effect of enabling stack lift, but assuming that's not a problem, one of several no-ops is STO ST X.

EDIT: "Several?" There aren't actually that many. The others I remember are X<> ST X and ├"".
On the 41, "", a synthetic construct which looks like it should clear the alpha register, is actually a no-op as well, and it's the only one that is one byte. I forget what it does on the 42S...