The five symmetry elements have associated with them five types of symmetry operation, which leave the geometry of the molecule indistinguishable from the starting geometry. They are sometimes distinguished from symmetry elements by a caret or circumflex. Thus, Ĉ n is the rotation of a molecule around an axis and Ê is the identity operation. A symmetry element can have more than one symmetry operation associated with it. For example, the C 4 axis of the square xenon tetrafluoride (XeF 4) molecule is associated with two Ĉ 4 rotations in opposite directions (90° and 270°), a Ĉ 2 rotation (180°) and Ĉ 1 (0° or 360°). Because Ĉ 1 is equivalent to Ê, Ŝ 1 to σ and Ŝ 2 to î, all symmetry operations can be classified as either proper or improper rotations.