t ^ ^ = { v r − − ( v r ⋅ ⋅ n ^ ^ ) n ^ ^ | v r − − ( v r ⋅ ⋅ n ^ ^ ) n ^ ^ | v r ⋅ ⋅ n ^ ^ ≠ ≠ 0 f e − − ( f e ⋅ ⋅ n ^ ^ ) n ^ ^ | f e − − ( f e ⋅ ⋅ n ^ ^ ) n ^ ^ | v r ⋅ ⋅ n ^ ^ = 0 f e ⋅ ⋅ n ^ ^ ≠ ≠ 0 0 v r ⋅ ⋅ n ^ ^ = 0 f e ⋅ ⋅ n ^ ^ = 0