# Superposition in math

##### Junior Member
to be more direct and sorry for my light English writing, lets assume you have X is integer and Y is integer, so we are considering also X+Y is integer in general, I mean the component X+Y also integer although it has "+" in its term ..so my question how it's integer? like wise in analogy of X [type of something] + Y[type of something] I can relate to the term "X+Y" also as [Type of something] but why I can relate to the term although it has + between X and Y as a [Type of something] ? thanks.

#### Otis

##### Senior Member
to be more direct … X is integer and Y is integer …

… [consider] X+Y is integer …

… so my question how it's integer? …
X+Y is an Integer because the set of Integers is closed under addition.

thanks alot!!