Definition:Set Union/Historical Note
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Historical Note on Set Union
The concept of set union, or logical addition, was stated by Leibniz in his initial conception of symbolic logic.
The symbol $\cup$, informally known as cup, was first used by Hermann Günter Grassmann in Die Ausdehnungslehre from $1844$.
However, he was using it as a general operation symbol, not specialized for set union.
It was Giuseppe Peano who took this symbol and used it for union, in his $1888$ work Calcolo geometrico secondo l'Ausdehnungslehre di H. Grassmann.
Peano also created the large symbol $\bigcup$ for general union of more than two sets.
This appeared in his Formulario Mathematico, 5th ed. of $1908$.
Sources
- 1992: George F. Simmons: Calculus Gems ... (previous) ... (next): Chapter $\text {A}.19$: Leibniz ($\text {1646}$ – $\text {1716}$)
- Earliest Uses of Symbols of Set Theory and Logic in Jeff Miller's website Earliest Uses of Various Mathematical Symbols