Yes. When we implemented 6-D Ferret we didn't want to make the names E, F, M, and N into reserved pseudo-variable names, akin to X,Y, I, J, etc. Existing scripts use some of those as variable names, and we didn't want to have "LET n = ..." suddenly become an invalid command. So the pseudo-variables in the E and F directions are therefore _E, _F, _M, and _N. And for symmetry, you can also use an underscore before any of the other direction variables, _X or _K.
Here's the whole scoop on pseudo-variable names:
On 5/2/2018 8:15 AM, Ryo Furue wrote: