In search of a solution, to rewrite an one-parameter GET Request as virtual sub-folders, limiting it to specific values, I concluded to write the above Apache .htaccess rewrite rule.
This script, rewrite the value of the parameter named
id, with the accepted values
c as virtual sub-folders of a destination.
RewriteEngine On RewriteRule ^(a|b|c)\/?$ /?id=$1 [L]
http://myhost.com/arewrited also as
http://myhost.com/dis not rewrited