E103 - Duplicate group label, edge, or group membership

Cause

One of three deck-level uniqueness invariants was violated: two groups share the same group: label; the same edge appears twice (same endpoints and sides); a single slide is listed under two different groups.

Example

{ slides: [
  { group: "demos", slides: ["a"] },
  { group: "demos", slides: ["b"] }   // duplicate group label
]}

How to fix

Rename duplicate group labels; remove the duplicate edge from the edges: list; assign each slide to at most one group.