Apply overload selection followed by dynamic dispatch: method overloading chooses a signature from the receiver's static type and argument static types, then dynamic dispatch chooses an override of that signature using the receiver's runtime type. A super call selects the inherited implementation; a call on the companion object B uses that object's own methods.[ref]
The output, in order, is
f(x:X) in B
f(y:Y) in A
f(x:X) in A, g(x:X) in B
f(x:X) in ObjB, g(y:Y) in ObjB, h(y:Y) in B, h(z:Z) in C
f(y:Y) in C, m(a:A) in Y, k(x:X) in C
For a.f(x), the argument's static type is X, selecting f(X); the receiver's runtime type B selects B.f(X). For a.f(z), the receiver's static type A exposes only f(X) and f(Y). The Z argument fits both, and f(Y) is more specific. B does not override that signature, so A.f(Y) runs. The additional overload B.f(Z) is invisible through a.
For c.g(z), the inherited instance B.g(X) calls super.f(x), which is A.f(X). For c.h(z), method overloading selects C.h(Z). Its super.h(z) calls B.h(Y), where the local parameter has static type Y. Consequently B.g(y) selects g(Y) on the companion object, whose only f signature is f(X).
Finally, c.k(x) calls x.m(this). The receiver x has runtime type Y, so dynamic dispatch enters Y.m(A). Inside that method, this has static type Y, selecting a.f(Y); the actual argument object is c, so dynamic dispatch reaches C.f(Y). Therefore
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Write each Scala trait linearization from most specific to least specific. Merge the parents' Scala trait linearizations right-to-left, removing a duplicate from the earlier portion when it also appears in the later portion. This retains every base once while respecting its required position after derived traits.[ref]
CityMan, City, Earth, Man, Mammal, Animal, Describe

BirdMan, City, Earth, Man, Mammal, Bird, Animal, Describe

BatMan, Man, Gotham, City, US, Earth, Bat, Mammal, Bird, Animal, Describe
For example, combining the final City with Gotham does not put City before its derived trait Gotham; duplicate removal places it after Gotham. Similarly Mammal and Bird remain after Bat, despite their occurrence through other parents.
Each describe calls super.describe before appending its own label. Thus execution enters implementations along the displayed Scala trait linearization, and appends labels in reverse order when calls return. The three printed lines are
Describe, Animal, Mammal, Man, Earth, City, 
Describe, Animal, Bird, Mammal, Man, Earth, City, 
Describe, Animal, Bird, Mammal, Bat, Earth, US, City, Gotham, Man,
Each line has a final comma and space, because every printed string fragment includes them. The essential result is
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