  The "rigid bodies" must be in Relativity the "deformable bodies" where the
longitudinal waves propagate with the maximun speed $c$. In 1909, Born studied
the "relativistic underformable body" but made the mistake of calling it
"rigid". The "rigid body" one can find in all Relativity books is, in fact,
Born's "undeformable body" of 1909. This error was at the origin of a lot of
difficulties and paradoxes not yet clarifed in any relativity book. The
"relativistic elastic laws for rigid bodies in one dimension" were discovered
by Mc Crea, in 1952, and by A.Brotas, in 1968. The generalization of these laws
for 2 and 3 dimensions resolve all those paradoxes. We propose the introdution
of these laws in the elementary courses of Relativity.
