When X is a finite set {1, ..., n}, the inverse semigroup of one-to-one partial transformations is denoted by Cn and its elements are called charts or partial symmetries.4 The notion of chart generalizes the notion of permutation. A (famous) example of (sets of) charts are the hypomorphic mapping sets from the reconstruction conjecture in graph theory.5
The cycle notation of classical, group-based permutations generalizes to symmetric inverse semigroups by the addition of a notion called a path, which (unlike a cycle) ends when it reaches the "undefined" element; the notation thus extended is called path notation.6
Grillet, Pierre A. (1995). Semigroups: An Introduction to the Structure Theory. CRC Press. p. 228. ISBN 978-0-8247-9662-4. 978-0-8247-9662-4 ↩
Hollings 2014, p. 252 - Hollings, Christopher (2014). Mathematics across the Iron Curtain: A History of the Algebraic Theory of Semigroups. American Mathematical Society. ISBN 978-1-4704-1493-1. ↩
Ganyushkin & Mazorchuk 2008, p. v - Ganyushkin, Olexandr; Mazorchuk, Volodymyr (2008). Classical Finite Transformation Semigroups: An Introduction. Springer. doi:10.1007/978-1-84800-281-4. ISBN 978-1-84800-281-4. https://doi.org/10.1007%2F978-1-84800-281-4 ↩
Lipscomb 1997, p. 1 - Lipscomb, S. (1997). Symmetric Inverse Semigroups. AMS Mathematical Surveys and Monographs. American Mathematical Society. ISBN 0-8218-0627-0. ↩
Lipscomb 1997, p. xiii - Lipscomb, S. (1997). Symmetric Inverse Semigroups. AMS Mathematical Surveys and Monographs. American Mathematical Society. ISBN 0-8218-0627-0. ↩