Consider a Lorentz boost in a fixed direction "z". This can be interpreted as a rotation of the time axis into the "z" axis, with an imaginary rotation parameter. If this rotation parameter were real, it would be possible for a 180° rotation to reverse the direction of time and of "z". Reversing the direction of one axis is a reflection of space in any number of dimensions. If space has 3 dimensions, it is equivalent to reflecting all the coordinates, because an additional rotation of 180° in the "x-y" plane could be included.