**Function:**`INTERVAL_VECTOR LSS (MATRIX`

`A`, VECTOR`b`, BOOL &`ok`)- Computes an enclosure of the solution set
`x`of the linear system`A``x`=`b`. If the enclosure is possible, it is returned and`ok`is set to`TRUE`

. Otherwise`ok`is set to`FALSE`

and the return value is undefined.

**Function:**`INTERVAL_VECTOR ILSS (INTERVAL_MATRIX`

`A`, INTERVAL_VECTOR`b`, BOOL &`ok`)- Computes an enclosure of the solution set
`x`of the linear system`A``x`=`b`. If the enclosure is possible, it is returned and`ok`is set to`TRUE`

. Otherwise`ok`is set to`FALSE`

and the return value is undefined.