University Mathematics Handbook (2015)
XII. Complex Functions
Chapter 8. Behavior of Analytical Functions at Infinity
a. Point 
is said to belong to 
– neighborhood of 
if 
belongs to 
- neighborhood of 
.
b. Function 
is analytic in the neighborhood of 
, if function 
is analytic in the neighborhood of .
c. is a removable singular point, a pole or an essential singular point of function if is a removable singular point, a pole or an essential singular point of function , respectively.