Hi,
In section 2.5 Structure Definitions of the Typed Racket Reference, there is an example of a substructure:
Examples:
> (struct (X Y) 2-tuple ([first : X] [second : Y]))
> (struct (X Y Z) 3-tuple 2-tuple ([first : X] [second : Y] [third : Z]))
I presume the correct definition of 3-tuple should be:
(struct (X Y Z) 3-tuple 2-tuple ([third : Z]))
Best,
António.