How to do arithmetic in the type system?

[nilshg]

Instead of copying the answers from the previous discussion, I’ll just link it:

Parametric type with numbers

Hello! I am having difficulties trying to model the adequate code for what I want to achieve. Imagine I have the following struct: struct Device a::NTuple{3,Float64} b::NTuple{2,Float64} end where b is always going to be one element shorter than a. How can I generalize this for N? I figured that it would be something like struct Device{N} a::NTuple{N,Float64} b::NTuple{N-1,Float64} end but it errors because I cannot perform substraction on types. Thanks!