Let's say I have a model like
A = α0 + α1*B + α2*C + α3*D + ϵ (Model 1)
Then I can estimate it's nested models
A = α0 + α1*B + α2*C + ϵ (Model 2)
A = α0 + α1*B + ϵ (Model 3)
If models 2 and 3 are nested models of model 1, what is model 1 to models 2 and 3?
In other words, if i can call models 2 and 3 nested models of model 1, how would i call a model 4 (which is an extension of model 1) defined as:
A = α0 + α1*B + α2*C + α3*D + α4*E + ϵ (Model 4)
Are nested models just those, which are subset of some larger model, or can i call even model extensions "nested models"?