“There are two ways of ridding ourselves of a thing which burdens us, casting it away or letting it fall. To cast away requires an effort of which we may not be capable, to let fall imposes no labour, is simpler, without peril, within reach of all. To cast away, again, implies a certain interest, a certain animation, even a certain fear; to let fall is absolute indifference, absolute contempt; believe me, use this method, and Satan will flee.” ― Joris-Karl Huysmans, En Route
Is to let fall is absolute indifference, absolute contempt a complete sentence? A complete sentence I think requires a verb and an argument. is seems a verb here, but I do not see a noun or subject. to let fall almost seems like an infinitive phrase. I have frequently seen infinitive phrases like To win at chess. In such phrase, is to a preposition, win an infinitive verb, at another preposition, and chess a noun?
But I don't get it —It seems that in my sample above, to is a preposition followed by two verbs let and fall. If so, what would be the subject of the clause?