What is the preposition in "today, by royal proclamation, is market day"?

A preposition is defined as an "a word governing, and usually preceding, a noun or pronoun and expressing a relation to another word or element in the clause." Therefore, the word that links the parts of the sentence is "by." The clause "by royal proclamation" is considered as the prepositional phrase in the sentence.

In 2081, everyone is equal not only in the eyes of the law but in every way; nobody is smarter, more athletic, better looking, etc. than anyone else. hazel is of average intelligence, which means she can't think about anything except in short bursts, and george has an intelligence way above normal.