WordPress Multisite with NGINX, subfolders, and FROM a subfolder

Actually, I solved it thanks to this reference:
https://rtcamp.com/wordpress-nginx/tutorials/multisite/subdirectories/in-a-subdirectory/

With the root directory of the installation being “labs” in my case, the final nginx configuration file looks like:

# You may add here your
# server {
#   ...
# }
# statements for each of your virtual hosts to this file

##
# You should look at the following URL's in order to grasp a solid understanding
# of Nginx configuration files in order to fully unleash the power of Nginx.
# http://wiki.nginx.org/Pitfalls
# http://wiki.nginx.org/QuickStart
# http://wiki.nginx.org/Configuration
#
# Generally, you will want to move this file somewhere, and start with a clean
# file but keep this around for reference. Or just disable in sites-enabled.
#
# Please see /usr/share/doc/nginx-doc/examples/ for more detailed examples.
##

server {
    listen 80 default_server;
    listen [::]:80 default_server ipv6only=on;

    root /var/www/public;
    index index.php index.html index.htm;

    # Make site accessible from http://localhost/
    server_name whatever.com;
    # include hhvm.conf;

    # Rewrite multisite '.../wp-.*' and '.../*.php'.
    if (!-e $request_filename) {
        rewrite /wp-admin$ $scheme://$host$uri/ permanent;
        rewrite ^/labs(/[^/]+)?(/wp-.*) /labs$2 last;      
        rewrite ^/labs(/[^/]+)?(/.*\.php)$ /labs$2 last;
    }


    location /labs/ {
        # First attempt to serve request as file, then
        # as directory, then fall back to displaying a 404.
        try_files $uri $uri/ /labs/index.php?$args;
    }


    location ~ \.(hh|php)$ {
        try_files $uri /labs/index.php;
        fastcgi_keep_conn on;
        fastcgi_pass   127.0.0.1:9000;
        fastcgi_index  index.php;
        fastcgi_param  SCRIPT_FILENAME $document_root$fastcgi_script_name;
        include        fastcgi_params;
    }

    location ~* ^.+\.(ogg|ogv|svg|svgz|eot|otf|woff|mp4|ttf|rss|atom|jpg|jpeg|gif|png|ico|zip|tgz|gz|rar|bz2|doc|xls|exe|ppt|tar|mid|midi|wav|bmp|rtf)$ {
        access_log off; log_not_found off; expires max;
    }

    location = /robots.txt { access_log off; log_not_found off; }
    location ~ /\. { deny  all; access_log off; log_not_found off; }


}

And it works just fine. Thank you very much for your help!