A topological space has this property if and only if there exist disjoint neighborhoods around any two disjoint points in the space. Urysohn’s lemma (-5[1])gives necessary and sufficient conditions for a topological space to have this property. The Frenet-Serret (-5[1])(“freh-NAY seh-RAY”) frame contains two objects named for this property. The left (15[2])and right (15[1])cosets of a (*) subgroup with this property are necessarily equal, so quotient groups may only be constructed over a subgroup with this property. Groups with this property are invariant under conjugation. The final step in the Gram-Schmidt process is to divide all the outputted orthogonal vectors by their magnitude so that they have this property. For 10 points, identify this word which describes vectors that are perpendicular to a given surface. ■END■