Corrigendum (correctif)

 A commenter pointed out that he didn't understand something, and the fault certainly lies with me, I made a notation error by writing M(R)={60,0,0,0) instead of M (R)={0,0,60,0).
 The distance of 60 meters is to be noted in z, not in x.
 I am therefore putting back the corrected image, and I ask any readers to apologize for this error which I am correcting on a new .png
  <http://news2.nemoweb.net/jntp?uiPV8wIoabki7MzQ4u7qHbNbjuo@jntp/Data.Media:1>
  Well.
  What is M'(R')={x',y',z', 0}
  R.H. --
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