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# Redirect knowing the key "cevpage" is NOT in the query string
RewriteCond %{REQUEST_URI} !\.[a-z]+$|[A-Z]+$
RewriteCond %{QUERY_STRING} !cevpage=|&cevpage|^cevpage
RewriteRule (.*) index.php?cevpage=$1 [QSA]

# Redirect knowing the key "cevpage" IS in the query string
RewriteCond %{REQUEST_URI} !\.[a-z]+$|[A-Z]+$
RewriteCond %{QUERY_STRING} cevpage=|&cevpage|^cevpage
RewriteRule (.*) index.php [QSA]