The following currently typechecks:
constructor of C
interface constructor(uint24 _x)
creates
uint24 x := _x
behaviour increase of C
interface increase(uint24 new_x)
storage
x => new_x
behaviour increase of C
interface increase2(uint24 new_x)
storage
x => new_x + 1
But it should fail since we have two behaviours of the same name.