Infinities.

The arithmetic operations of Erable accept infinity arguments. The $+\infty$ symbol may be obtained from the keyboard by $\alpha$-right shift-I in normal mode or $\alpha$-right shift-DEL in user mode followed by ENTER. The $-\infty$ symbol is obtained by hitting the quote key, the - key and $\alpha$-right shift-I or $\alpha$-right shift-DEL followed by ENTER. $\infty$ and $-+\infty$ are understood as unsigned infinity (with the following exception: $\infty$ is understood as $+\infty$ in a bound of an integral or in a LIMIT instruction). The ? symbol means that the result of an operation is undefined. All operations involving ? will return ? after simplifications.

Remark 7   The current release returns ? for some expressions which are not undetermined, like $(+\infty )^{-\infty }$.

Be aware of the fact that arithmetic operations on infinities may return false answers because Erable can not check for nullity if non rational expressions are encoutered. For example $(\sin(2x)-2\sin(x)\cos(x))/0$ will return $\infty$ instead of 0. This remark applies to the LIMIT instruction too (call SERIES if the answer of LIMIT seems false).