[overpass] Get all ways which aren't part of a specific relation

I'm trying to write an Overpass query to get all ways (filtered with a specific tag) which aren't included in a relation (with a specific tag).

Here is my query (edited after maxerickson's answer): https://overpass-turbo.eu/s/HXj

// Collect all ways with piste:type=nordic and store the result in a variable .all
way({{bbox}})["piste:type"="nordic"]->.all;

// Select all relations, where one of the ways in variable .all is a member
rel["piste:type"="nordic"](bw.all);
// ...and for those relations find all related way members
way(r);

// Calculate the set difference (._ contains all nodes which are member of a relation)
( .all; - ._; );

// return the result including meta data
out meta;

I followed this example, it's pretty close of what I want to do but for nodes, so I just changed a few things to get ways instead of nodes.

Unfortunately my query doesn't return anything. Do you see anything wrong in my query?

Edit after some debugging:

here a way that the query should return (has a piste:typenordic tag and isn't part of a piste:type=nordic relation): https://www.openstreetmap.org/way/475719899

• the way is returned if I tell Overpass to display the .all set: https://overpass-turbo.eu/s/HXh → good
• the way isn't returned when I search for all way that are part of a relation (lines 5-7): https://overpass-turbo.eu/s/HXi → good
• so I guess the problem is on the difference between the 2 sets (line 10): why the way 475719899 is removed if it isn't in the ._ set?

Thanks!