aptitude install steam
Note: selecting "steam:i386" instead of the
      virtual package "steam"
The following NEW packages will be installed:
  gcc-4.9-base{a} gcc-4.9-base:i386{a} libaudit-common{ab} libaudit1{a}
  libdrm-intel1:i386{a} libdrm-nouveau2{a} libdrm-nouveau2:i386{a}
  libdrm-radeon1:i386{a} libdrm2:i386{a} libegl1-mesa{a}
  libegl1-mesa-drivers{a} libelf1:i386{a} libepoxy0{a} libffi6{a}
  libffi6:i386{a} libgbm1{a} libgl1-mesa-dri:i386{a}
  libgl1-mesa-glx:i386{a} libglapi-mesa:i386{a} libllvm3.4{a}
  libllvm3.4:i386{a} libopenvg1-mesa{a} libpciaccess0:i386{a}
  libtinfo5:i386{a} libtxc-dxtn-s2tc0{a} libtxc-dxtn-s2tc0:i386{a}
  libudev1{a} libudev1:i386{a} libwayland-client0{a}
  libwayland-egl1-mesa{a} libwayland-server0{a} libxcb-dri2-0:i386{a}
  libxcb-dri3-0{a} libxcb-dri3-0:i386{a} libxcb-glx0:i386{a}
  libxcb-present0{a} libxcb-present0:i386{a} libxcb-sync1{a}
  libxcb-sync1:i386{a} libxcb-xfixes0{a} libxdamage1:i386{a}
  libxfixes3:i386{a} libxinerama1:i386{a} libxshmfence1{a}
  libxshmfence1:i386{a} libxxf86vm1:i386{a} steam:i386
The following packages will be REMOVED:
  libdrm-nouveau1a{u}
The following packages will be upgraded:
  libgl1-mesa-dri libgl1-mesa-glx libglapi-mesa libstdc++6 libstdc++6:i386
  xserver-common xserver-xorg-core
7 packages upgraded, 47 newly installed, 1 to remove and 984 not upgraded.
Need to get 35.3 MB/37.0 MB of archives. After unpacking 81.1 MB will be used.
The following packages have unmet dependencies:
 xserver-xorg-video-apm : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-ark : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-ati : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-openchrome : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-s3virge : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-mga : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-chips : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-mach64 : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-trident : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-sis : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-siliconmotion : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-input-vmmouse : Depends: xorg-input-abi-16 which is a virtual package.
 xserver-xorg-video-savage : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-tdfx : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-nvidia : Depends: xorg-video-abi-15 which is a virtual package. or
                                      xorg-video-abi-14 which is a virtual package. or
                                      xorg-video-abi-13 which is a virtual package. or
                                      xorg-video-abi-12 which is a virtual package. or
                                      xorg-video-abi-11 which is a virtual package. or
                                      xorg-video-abi-10 which is a virtual package. or
                                      xorg-video-abi-8 which is a virtual package. or
                                      xorg-video-abi-6.0 which is a virtual package.
                             Depends: xserver-xorg-core (< 2:1.15.99) but 2:1.16.0-1 is to be installed.
 xserver-xorg-video-intel : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-vmware : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-r128 : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-input-evdev : Depends: xorg-input-abi-16 which is a virtual package.
 xserver-xorg-video-vesa : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-s3 : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-voodoo : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-fbdev : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-input-wacom : Depends: xorg-input-abi-16 which is a virtual package.
 xserver-xorg-video-nouveau : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-neomagic : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-input-mouse : Depends: xorg-input-abi-16 which is a virtual package.
 xserver-xorg-video-sisusb : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-tseng : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-radeon : Depends: xorg-video-abi-12 which is a virtual package.
 libaudit-common : Breaks: libaudit0 but 1:1.7.18-1.1 is installed.
 xserver-xorg-video-cirrus : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-input-synaptics : Depends: xorg-input-abi-16 which is a virtual package.
 xserver-xorg-video-rendition : Depends: xorg-video-abi-12 which is a virtual package.
 xserver-xorg-video-i128 : Depends: xorg-video-abi-12 which is a virtual package.
The following actions will resolve these dependencies:

      Remove the following packages:
1)      nvidia-glx
2)      task-desktop
3)      task-gnome-desktop
4)      xorg
5)      xserver-xorg
6)      xserver-xorg-core
7)      xserver-xorg-input-all
8)      xserver-xorg-input-evdev
9)      xserver-xorg-input-mouse
10)     xserver-xorg-input-synaptics
11)     xserver-xorg-input-vmmouse
12)     xserver-xorg-input-wacom
13)     xserver-xorg-video-all
14)     xserver-xorg-video-apm
15)     xserver-xorg-video-ark
16)     xserver-xorg-video-ati
17)     xserver-xorg-video-chips
18)     xserver-xorg-video-cirrus
19)     xserver-xorg-video-fbdev
20)     xserver-xorg-video-i128
21)     xserver-xorg-video-intel
22)     xserver-xorg-video-mach64
23)     xserver-xorg-video-mga
24)     xserver-xorg-video-neomagic
25)     xserver-xorg-video-nouveau
26)     xserver-xorg-video-nvidia
27)     xserver-xorg-video-openchrome
28)     xserver-xorg-video-r128
29)     xserver-xorg-video-radeon
30)     xserver-xorg-video-rendition
31)     xserver-xorg-video-s3
32)     xserver-xorg-video-s3virge
33)     xserver-xorg-video-savage
34)     xserver-xorg-video-siliconmotion
35)     xserver-xorg-video-sis
36)     xserver-xorg-video-sisusb
37)     xserver-xorg-video-tdfx
38)     xserver-xorg-video-trident
39)     xserver-xorg-video-tseng
40)     xserver-xorg-video-vesa
41)     xserver-xorg-video-vmware
42)     xserver-xorg-video-voodoo

      Keep the following packages at their current version:
43)     libaudit-common [Not Installed]
44)     libaudit1 [Not Installed]

      Leave the following dependencies unresolved:
45)     gdm3 recommends xserver-xorg
46)     nvidia-kernel-dkms recommends nvidia-glx (>= 304.117)