On the paragraph explaining arithmetic expansion, Bash's user guide uncovers 2 different ways of evaluating an expression, the first one uses $((?EXPRESSION?)) and the second one uses $[?EXPRESSION?]. The two ways seem pretty similar as the only difference I have found is:

$[?EXPRESSION?] will only calculate the result of EXPRESSION, and do no tests:

Yet, I am intrigued because the same document recommends using $[?EXPRESSION?] rather than $((?EXPRESSION?)).

Wherever possible, Bash users should try to use the syntax with square brackets:

Why would you want that if less tests are being done?