How to derive the set notation from regular expressions?

Question

I have a language $L$ with some context-free grammer which generates the following strings:

def
dededefff
dedeff
dedededeffff
dededededefffff

Im trying to come up with some set definition of that example, however struggle to finde the appropriate set:

$L = \{(d,e,f)\ |\ d\in L\wedge e\in L\wedge f \in L\}$

Where:

S → DESF | DEF
D → d
E → e
F → f

is K and

$G = (\{S, D, E, F\}, \{d, e,f\}, K, S)$ the context free grammer

Answer 1

Perhaps the following: $$\{(de)^nf^n\mid n \in \mathbb{N}\}$$