TITLE: First usage of the symbol ∈
QUESTION [8 upvotes]: Concerning a book [1] I am reading the symbol $\in$ was first used by Giuseppe Peano and is the first letter $\epsilon$ (epsilon) of the word ἐστί (means "is"). Does anyone know in which work of Peano $\in$ was first used?
[1] Ingmar Lehmann, Wolfgang Schulz: "Mengen, Relationen, Funktionen" (3. Auflage, 2007), page 10
Similar question: What is the name of the ∈ symbol and where does it come from?

REPLY [3 votes]: Concerning https://de.wikipedia.org/wiki/Elementzeichen#Geschichte it was first used 1889 in the work Arithmetices principia nova methodo exposita (page X):

„Signum ϵ significat est. Ita a ϵ b legitur a est quoddam b“

This means something like (my translation which isn't the best!):

The symbol ϵ means is. So a ϵ b has to be read as a is a b

Here is a link to the work: https://archive.org/details/arithmeticespri00peangoog
The quoted sentence in the original work: