SELECT count(*) FROM web_client_accelerator WHERE id NOT IN ( SELECT accelerator_id FROM accelerator_compatible_browser );
How many accelerators are not compatible with the browsers listed ?
[Schema (values) (types)]: | browser_web |  Web_client_accelerator : id (text) , name (number) , operating_system (text) , client (text) , connection (text) | browser : id (text) , name (number) , market_share (text) | accelerator_compatible_browser : accelerator_id (text) , browser_id (number) , compatible_since_year (text);