DOC: add link to "Indexing dif/2" in DocLog format
+/** Predicates from [*Indexing dif/2*](https://arxiv.org/abs/1607.01590).
+
+Example:
+
+```
+?- tfilter(=(a), [X,Y], Es).
+ X = a, Y = a, Es = "aa"
+; X = a, Es = "a", dif:dif(a,Y)
+; Y = a, Es = "a", dif:dif(a,X)
+; Es = [], dif:dif(a,X), dif:dif(a,Y).
+```
+*/
+
:- module(reif, [if_/3, (=)/3, (',')/3, (;)/3, cond_t/3, dif/3,
memberd_t/3, tfilter/3, tmember/2, tmember_t/3,
tpartition/4]).
