pub fn prev(&self) -> Result<EdgeIndex, BvError> {
        self.prev_().ok_or_else(|| {
            BvError::InternalError("The edge does not have a previous edge".to_string())
        })
    }
/// returns the previous edge (counter clockwise winding)
returns the previous edge (counter clockwise winding)
returns the previous edge ( counter clockwise winding )
pub fn prev(&self) -> Result<EdgeIndex, BvError> {
        self.prev_().ok_or_else(|| {
            BvError::InternalError("The edge does not have a previous edge".to_string())
        })
    }
pub fn prev ( & self ) -> Result < EdgeIndex , BvError > { self . prev_ ( ) . ok_or_else ( | | { BvError :: InternalError ( " " . to_string ( ) ) } ) }
returns the previous edge (counter clockwise winding)
returns the previous edge ( counter clockwise winding )
&self