I have tried with module Global Redirect and I have achieved the desired results. I had thought it eliminated erroneously duplicated URLs, but it seems that it goes further to "hide" system path if an alias-url is set.
The problems stated in the documentation page itself, about incompatibilities with multilingual sites: I had found a problem of infinite reloop, but it was my fault; it was caused by a directory named "en" which is a very bad idea if you have languages set at suffixes in the URL, so it will cause the path to be www.example.com/en/ instead of www.example.com/en , thus doing an infinite loop.