"Frink tries to be smart about this, and will in some cases rewrite interval arithmetic to avoid overdetermination, even when you want the intervals to be different."
To be fair, if you use Frink's recommended "new interval" syntax instead of defining your own function i[min,max] as a wrapper, Frink won't rewrite your expression.
There are some deeper technical reasons for this but a "new" expression is never considered equal to another "new" expression during mathematical simplification.
The page says:
"Frink tries to be smart about this, and will in some cases rewrite interval arithmetic to avoid overdetermination, even when you want the intervals to be different."
To be fair, if you use Frink's recommended "new interval" syntax instead of defining your own function i[min,max] as a wrapper, Frink won't rewrite your expression.
There are some deeper technical reasons for this but a "new" expression is never considered equal to another "new" expression during mathematical simplification.
Citation: I am the author of Frink LOL