-6 6 setxrange
-6 6 setyrange

50 setxunit
/ScreenDist .3 def
2 setlinejoin

10 18 10 SetCamPos
0 0 0 SetCamView

/eq1 [0 0 1 -1]  def
/eq2 [0 0 1 -1]  def
/eq3 [0 0 1 1]  def
/eq4 [1 0 1 0] def

%% plan d equation z = 1
eq1 eq2plan
newplan
dup eq4 solideqplansepare
dup (blanc) solidputcolors
/Plan1a exch def
dup (blanc) solidputcolors
/Plan1b exch def

%% plan d equation z = 0
eq2 eq2plan
newplan
dup eq4 solideqplansepare
dup (blanc) solidputcolors
/Plan2a exch def
dup (blanc) solidputcolors
/Plan2b exch def

%% plan d equation z = -1
eq3 eq2plan
newplan
dup eq4 solideqplansepare
dup (blanc) solidputcolors
/Plan3a exch def
dup (blanc) solidputcolors
/Plan3b exch def

%% plan d equation x + y + 1 = 0
eq4 eq2plan
newplan
dup (cyan) solidputcolors
/Plan4 exch def

Plan3a drawsolid*
Plan2a drawsolid*
Plan4 drawsolid*
Plan3b drawsolid*
Plan2b drawsolid*
pointilles
Plan3a drawsolid
Plan2a drawsolid