NestAssociatedTypeTest.swift

protocol Animal {
    associatedtype H: Human
    
    func action(by human: H)
}

protocol Human {
    associatedtype A: Animal
}

class Man<T: Animal>: Human {
    typealias A = T
    
    var animal: A
    
    init(animal: A) {
        self.animal = animal
    }
    
    func foo() {
        self.animal.action(by: self as! A.H)
    }
}

class Cat: Animal {
    typealias H = Man<Cat>
    
    func action(by human: Man<Cat>) {
        print("fuck")
    }
}

Man<Cat>(animal: Cat()).foo()