Which notation ($\subset$ or $\subseteq$) was preferred by Bourbaki for set inclusion (not proper)?
A side question: Was the notation for subset one of the many notations invented by Bourbaki?
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Which notation ($\subset$ or $\subseteq$) was preferred by Bourbaki for set inclusion (not proper)?
A side question: Was the notation for subset one of the many notations invented by Bourbaki?
Best Answer
See :
See English translation :
Regarding origins :
In addition, Schröder uses $=$ superposed to $\subset$ for untergeordnet oder gleich, i.e. $\subseteq$; see Vorlesungen.
Giuseppe Peano, in Arithmetices Principia Novo Methodo Exposita (1889), page xi, uses an "inverted C" for inclusion :
Note. It is worth noticing that in Peano there is the distinction between the relation : "to be an element of" ($\in$) and the relaion : "to be included into" ($\subset$).
This distinction is not present in Schröder.
According to Bernard Linsky, Russell’s Notes on Frege’s Grundgesetze Der Arithmetik from §53, in Russell, 26 (2006), page 127–66 :