<s>
The	O
Laguerre	B-General_Concept
formula	I-General_Concept
(	O
named	O
after	O
Edmond	O
Laguerre	O
)	O
provides	O
the	O
acute	O
angle	O
between	O
two	O
proper	O
real	O
lines	O
,	O
as	O
follows	O
:	O
</s>
<s>
Laguerre	B-General_Concept
formula	I-General_Concept
can	O
be	O
useful	O
in	O
computer	B-Application
vision	I-Application
,	O
since	O
the	O
absolute	O
conic	O
has	O
an	O
image	O
on	O
the	O
retinal	O
plane	O
which	O
is	O
invariant	O
under	O
camera	O
displacements	O
,	O
and	O
the	O
cross	O
ratio	O
of	O
four	O
collinear	O
points	O
is	O
the	O
same	O
for	O
their	O
images	O
on	O
the	O
retinal	O
plane	O
.	O
</s>
