**3.1.3. Type Ia Supernova Hubble Diagram**

The type Ia supernova Hubble diagram now reaches *z*
0.4-0.8.
It can be used to infer the mass density parameter and the cosmological
constant. As we discuss later (section 4.1)
the observation favours a low
and a positive .
If we take their formal errors,
< 0.1 is allowed only at three
sigma for a zero universe
(Riess et al. 1998;
Perlmutter et
al. 1999).
A zero open universe may not
be excluded yet if some allowance
is taken for systematic effects, but EdS geometry
is far away from the observation.
The best favoured value is approximately,