I'll try to be clear because this is not what I am looking for.
What I'm trying to do is to define a new command that takes one argument but has a different behaviour whether that argument is or is not specified.
Here's what I have so far :
\newcommand\Nk[1][k]{N_{#1}}
I want to be able to get :
if I enter
\Nk
if I enter
\Nk{i}
For now, with that second option I just get .
So here's my question : how can I get that behaviour I want ?
Thanks a lot.
$\Nk[i]$
in the invocation. Square brackets are used for optional arguments, which is the way you have defined\Nk
.