If `veca` `xx` (`vecb` `xx` `vecc` ) + `vecb` `xx` (`vecc` `xx` `veca` ) + `vecc` `xx` (`veca` `xx` `vecb` ) = `vecx``xx` ` ` `vecy` ) then
`vecx` = `vec0`
`vecy` = `vec0`
`vecx` and `vecy`are parallel
`vecx` = `vec0` or`vecy` = `vec0` or`vecx` and `vecy`are parallel