# How to define WordMorphism on an infinite alphabet ?

Let imagine I want to do a substitution on the set of all words written with natural numbers.

Example 1: replace every number with its square.

Example 2: make precise rules for substitution of letter in some finite subset of the alphabet and decide that all other letters will be deleted (replaced with empty).

It's not very clear for me from the doc whether this is actually allowed with the command `WordMorphism`

, but if it is, I would like to understand how to do it.