Synthesized answer
The provided passages do not specify the evidence the author provides in "Ficciones."
The description of the collection mentions that Borges "often uses the labyrinth as a literary device to expound his ideas on all aspects of human life and endeavor" [1]. However, it does not detail what specific evidence he presents to support these ideas or what those ideas are. The only specific story mentioned is "Tlön, Uqbar, Orbis Tertius" [1], but no information is given about its content or any evidence it might contain.
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
Title: Ficciones by Jorge Luis Borges Description: A collection of his short stories in which Borges often uses the labyrinth as a literary device to expound his ideas on all aspects of human life and endeavor. ---------- Contains: [Tlön, Uqbar, Orbis Tertius](https://openlibrary.org/works/OL444914W)