In objective-c we declare only as property without instance variable?

I’m reading about core data and I noticed (again) in application delegate file: where the we have only the decleration of properties without the instance variables. By googling around I found that: In Objective-C 2.0 on either of the modern runtimes (ie, Intel 64bit and ARM) properties can be added to classes ‘dynamically’ (that is,

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