Remark 4.3.1. The data of and the relations can be described graphically as follows:
We define a differential category
.
The objects of are pairs where
and
such that the following diagram commutes
(4.3.2)
is the
differential submodule of of
elements
such that the following diagram commutes
The composition of maps is defined by restricting that of
.
So, we have a faithful forgetful
functor .
Note that is strongly pretriangulated and idempotent-complete.
Remark 4.3.3. Assume admits a left adjoint . The data of the map
corresponds by adjunction to the data of a map
The commutativity of the diagrams (4.3.1) is equivalent to the commutativity of the
diagrams (4.2.1).
Assume the diagrams commute. We obtain a lax bi--representation on
(cf Β§4.2.1).
Let . We have an adjunction isomorphism
Let .
The object is in and
defines a fully faithful functor of differential
categories .
Assume now is invertible. The canonical map is
invertible. Let . Consider .
We have
As a consequence, the functor above is an isomorphism of differential categories
.