Écrire à l'aide de quantificateurs If every element of E is an element of F, then E is included in F.

Yes, your statement is correct. In set theory and in mathematics in general, if every element of set E is also an element of set F, then we say that set E is a subset of set F, and we denote it as E ⊆ F. In other words, E is included in F, and all the elements of E are contained within F.