define multi dimensional function for part of a set in GAMS

Question

I have a set i /1 to 6/, v/ v1v10/ , t /t1t5/; I am going to define a function f1 which uses i=3 to 10 for calculating for all t and v numbers of set and f2 which uses any i other than these, as below.

f1(i,v,t)=e=cost(i,v,t)$ (i=3 to 10) f2(i,v,t)=e=cost(i,v,t)$ (i is not (3 to 10))

This is to ask :how can I define these properly in GAMS? Thank you