§ Sheaves in geometry and logic 1.3: Characteristic functions of subobjects

    !
 S --> 1
 v     |
 |     | true
 v     v
 X---->2
  phi(S)

§ Subobject category

  S --i--> S'
   \      /
   m\    /m'
     v  v
      X

§ GG bundles

§ Sieves / Subobject classifiers of presheaves

§ Sieves