Undefined array key "HTTP_ACCEPT_LANGUAGE" /home/refseek1/public_html/search2/include/func-common.php:23

substr(): Passing null to parameter #1 ($string) of type string is deprecated /home/refseek1/public_html/search2/include/func-common.php:23

Undefined array key "HTTP_ACCEPT_LANGUAGE" /home/refseek1/public_html/search2/searchdoc.php:24

substr(): Passing null to parameter #1 ($string) of type string is deprecated /home/refseek1/public_html/search2/searchdoc.php:24

site:www.cse.salford.ac.uk/physics/gsmcdonald/M1A_01_Algebra_Foundation... - RefSeek
Try this search on: Bing, Google Scholar, or Amazon