func isLitOrSingle(seg segment) bool {
	if seg.wild {
		return !seg.multi
	}
	return seg.s != "/"
}

// describeConflict returns an explanation of why two patterns conflict.
func describeConflict(p1, p2 *pattern) string {
	mrel := p1.compareMethods(p2)
	prel := p1.comparePaths(p2)
	rel := combineRelationships(mrel, prel)
	if rel == equivalent {

		{"GET /a", "HEAD /", "matches more methods than HEAD /, but has a more specific path pattern"},
		{"POST /", "/a", "matches fewer methods than /a, but has a more general path pattern"},
	} {
		got := describeConflict(mustParsePattern(t, test.p1), mustParsePattern(t, test.p2))
		if !strings.Contains(got, test.want) {
			t.Errorf("%s vs. %s:\ngot:\n%s\nwhich does not contain %q",
				test.p1, test.p2, got, test.want)
		}
	}
}

	}

	mux.mu.Lock()
	defer mux.mu.Unlock()
	// Check for conflict.
	if err := mux.index.possiblyConflictingPatterns(pat, func(pat2 *pattern) error {
		if pat.conflictsWith(pat2) {
			d := describeConflict(pat, pat2)
			return fmt.Errorf("pattern %q (registered at %s) conflicts with pattern %q (registered at %s):\n%s",
				pat, pat.loc, pat2, pat2.loc, d)
		}
		return nil
	}); err != nil {
		return err