Functions – Select the 1st and then the following elements of a & # 39; list & # 39;


I'm using a mix span and part to try to extract the arguments of a function that I need.

I use a function like $ J ^ mu (1,2,3) $
and I will try to portray this as J[mu,Range[1,3]]or more generally for any index or any number of arguments, J[index_,Range[1,n_]],

I have to pick the first element each time, that is H. The index of this function, and then I have to select some consecutive elements of the list. I.E; I have to choose terms like J[index,2,3],

I tried with some variations of span in the partArgument, but I'm having trouble taking just the first variable and some extras.

In particular, I'm trying to program the Berends-Giele recursion relationship for n-gluons.

Any help would be appreciated.

Many Thanks.

To edit:

To show an example:

J[mu,1,2,3,4,5][[3;;5]]

gives a result of

J[2,3,4]

as expected. If I take;

J[mu,1,2,3,4,5][[1]]

I will get

mu

that is not as expected. What I want is something like saying;

J[mu,1,2,3,4,5][[1,3;;4]]

what would come back

J[mu,3,4]

Is that possible with span and part?