International
Tables for Crystallography Volume B Reciprocal space Edited by U. Shmueli © International Union of Crystallography 2010 
International Tables for Crystallography (2010). Vol. B, ch. 1.3, p. 32

The reverse operation from differentiation, namely calculating the `indefinite integral' of a distribution S, consists in finding a distribution T such that .
For all such that with , we must haveThis condition defines T in a `hyperplane' of , whose equationreflects the fact that ψ has compact support.
To specify T in the whole of , it suffices to specify the value of where is such that : then any may be written uniquely aswithand T is defined byThe freedom in the choice of means that T is defined up to an additive constant.