from typing import Dict, Set

def candidate_subs(nav: Dict[str, Dict])-> Set[str]:
    nav_sub_candidates: Set[str] = set()
    for label, data in (nav.get("cats") or {}).items():
        top_slug = (data or {}).get("slug")
        if not top_slug:
            continue
        for s in (data.get("subs") or []):
            sub_slug = (s.get("slug") or "").strip()
            if sub_slug:
                nav_sub_candidates.add(f"/{top_slug}/{sub_slug}")
    return nav_sub_candidates