Addition of relativistic velocities in arbitrary directions in four-dimensional space

A vectorial construction method for adding relativistic velocities in arbitrary directions with the aid of a fifth dimension is presented and justified. Sections: 1. Introduction 2. The special case of equal directions 3. Directions perpendicular to each other 4. Arbitrary acute angles between u' and v 5. Addition of the four-dimensional vectors u'* and v* 6. Obtuse angles between u' and v 7. Summary and outlook Attachment