Options +FollowSymlinks
RewriteEngine on
RewriteRule ^category\/(.+)\/.+\/?$ category.php?id=$1&filter=a [nc]
RewriteRule ^category/(.+)/(.+) category.php?id=$1&filter=$2 [nc]
RewriteRule ^item/(.+) item.php?id=$1 [nc]
RewriteRule ^index.html index.php