this `if` is confusing. I see it more like:

```ruby
if is_there_anybody_to_help?
# ...

private

def is_there_anybody_to_help?
  users_count > 1 ||
    users_count == 1 && !topic.users.include?(h.current_user.object)
end
```

as a bonus you receive quite sexy SQL query for checking if user is included in topic users