[Footnote: Cf. the complementary infinitive (28), equivalent to the
object of a verb, and the use of the infinitive after the prepositions
"por", "anstataux", "antaux ol" (98).]
Any modifier of the infinitive is necessarily adverbial. An indefinite
personal object (or pronominal complement of a preposition) after an
infinitive used as subject is expressed by the reflexive pronoun "si":
Promeni estas granda plezuro, to go walking is a great pleasure.
Promeni estas agrable, to go walking is pleasant.
Cxu estas facile rigardi la plafonon?
Is it easy to look at the ceiling?
Estas bone sin helpi, it is well to help oneself.
Paroli al si estas malsagxe, to talk to oneself is silly.