Prove Thomsen's Relation: for any lines
a,b
, and
c
, we have
R_(c)R_(a)R_(b)R_(c)R_(a)R_(b)R_(a)R_(b)R_(c)R_(a)R_(b)R_(c) \times R_(b)R_(a)R_(c)R_(b)R_(a)R_(b)R_(a)R_(c)R_(b)R_(a)=I,
where
I
is the identity transformation.