Shadow pairs

Flipping all four signs of a valid stack yields another valid stack (same letters). That twin’s ego ends are the first stack’s shadow ends. Sixteen stacks make eight pairs.

• Ne-Fi-Te-Si↔ Ni-Fe-Ti-Se
• Ne-Ti-Fe-Si↔ Ni-Te-Fi-Se
• Se-Fi-Te-Ni↔ Si-Fe-Ti-Ne
• Se-Ti-Fe-Ni↔ Si-Te-Fi-Ne
• Fe-Ni-Se-Ti↔ Fi-Ne-Si-Te
• Fe-Si-Ne-Ti↔ Fi-Se-Ni-Te
• Te-Ni-Se-Fi↔ Ti-Ne-Si-Fe
• Te-Si-Ne-Fi↔ Ti-Se-Ni-Fe