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Fatal error: Uncaught TypeError: mb_substr(): Argument #3 ($length) must be of type ?int, string given in /var/www/html/mathmod.org/prod/functions_and_classes/main.php:193 Stack trace: #0 /var/www/html/mathmod.org/prod/functions_and_classes/main.php(193): mb_substr() #1 /var/www/html/mathmod.org/prod/mods/STEP_Download.37.php(15): sDec() #2 /var/www/html/mathmod.org/prod/www/index.php(132): index() #3 {main} thrown in /var/www/html/mathmod.org/prod/functions_and_classes/main.php on line 193