Regular function

in a domain

A function $f(z)$ of a complex variable $z$ which is single-valued in this domain and which has a finite derivative at every point (see Analytic function). A regular function at a point $a$ is a function that is regular in some neighborhood of $a$.

References

[a1]	G. Springer, "Introduction to Riemann surfaces" , Addison-Wesley (1957) pp. 60; 169; 173