[racket] how must I interpreted this exercise

Hello,

I try to make this exercise :

Exercise 76: A programmer has chosen to represent locations as Cartesian 
points or just points:

    ;Location is one of:
    ;--Posn
    ;--Number
    ;interp. Posn are positions on the Cartesian grid,
    ;Numbers are positions on the number line

Design the function in-reach, which determines whether or not a given 
location's distance to the origin is strictly less than some constantR.

So I must design a function called in-reach.

Am I right I need to use two structs (Posn) . One for the given location 
and one for the origon ?

Regards,

Roelof



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