(b). The preposition el = of, out of, is sometimes omitted in such an expression as:—
Tri miaj parencoj = Three of my relatives (or, three relations of mine).
254. Prepositions as prefixes.—Prepositions are frequently used as prefixes, and when the compound word is a verb, the preposition is often repeated before the indirect complement of the verb.
Examples.—Mi eliris el la korto = I went out of the courtyard. Li eniris en la ĉambron = He entered (into) the room. La birdo deflugis de la arbo = The bird flew from the tree. Li eliris el la domo = He went out of the house. Or we could say, Li iris el la domo, omitting the joined preposition.
255. Prepositions and case.—In contrast to prepositions in English, which govern the accusative case, all prepositions in Esperanto govern the nominative case. If the complement of a preposition is in the accusative case, this is owing not to the preposition, but to the rule that the accusative is used to show the direction or place towards which movement (physical or otherwise) is made (par. [67]).
256. Preposition and the accusative of direction.—As already stated in par. [67], the accusative is used when direction (physical or otherwise) is implied towards something. But if the word towards which such movement is implied is the complement of a preposition, then such word is in the nominative or accusative, in accordance with the following rules:—
(a). If the preposition denotes of itself movement, its complement will be in the nominative, in accordance with Rule 8 that prepositions govern that case.
(b). If the preposition does not of itself denote movement, then movement is shown by placing its complement in the accusative (par. [67]).
257. Prepositions denoting movement.—The following two prepositions denote movement, and consequently their complement is never in the accusative:—Al = To, towards. Ĝis = Up to, as far as.
As regards the others, the following are those in general use, whose complement takes the accusative of direction when motion towards something is implied:—Antaŭ = Before. Ĉirkaŭ = Around, about. En = In. Kontraŭ = Against. Sub = Under. Super = Over. Sur = On, upon. Tra = Through. Trans = Across.