All your math.
All you functions.
XTRMTH uses easy-to-understand syntax, and won't force memorization of every edge-case.
All edge-cases* have a detailed, concice, error message. More broad errors will use formatted strings to show exactly where and how you messed up.
{Documentation to be added in version 2.0.0, along with xtrmth variables (xmv.py).}
*personally found or reported