RewriteEngine On

RewriteRule ^loesung/abschnitt-(.+?).html index.php?show=loesung&katalog=$1 [QSA]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-l
RewriteRule ^(.+?).html index.php?show=$1 [QSA]