An illustrative dataset---a matrix (of the dimensions 12x12) with a
monthly-based income (in EUR) of a local internet data provider with the
income structured by the customers subscribing within the given month (in 2023)
reported in the rows and monthly-based payments reported in columns.
The data matrix represents the incremental type of the run-off triangle.
data(xNetSubscribe)
A simple 12x12 (trangular) matrix of the class triangle with
twelve consecutive months (January 2023 -- December 2023) when new customers
subscribed to the stream service (rows) and monthly-based payments (columns)