An encircled version is encoded for use either as a symbol for acid-free paper or as an emoji. For instance, in mathematical expressions with summations and limits such as the one below: In mathematics, the infinity symbol is used more often to represent a potential infinity, rather than an actually infinite quantity as included in the extended real numbers, the ordinal numbers and the cardinal numbers (which use other notations). The open variant of the symbol is not used anymore and is not encoded as a separate character in Unicode.
Euler freely performed various operations on infinity, such as taking its logarithm. Leonhard Euler used an open variant of the symbol in order to denote 'absolutus infinitus'.
