week18.txt: found three illegal chars in iris

timeline/week18.txt

@@ -37,6 +37,10 @@ Week 18 (27.04.-03.05.)
 		   characters; the lowest of the range is 0xa0, which
 		   is below 0x7c (the pipe symbol)
 
+		-> the IRIs in the Isabelle exports have the following
+		   characters which are (according to automated tool
+		   `iriok' [4]) not valid: '|', '\' and ' '
+
 	[ ] run all quries from ulo paper in graphdb
 
 [ ] fix exported IRIs
@@ -56,3 +60,4 @@ References
 [1] https://www.w3.org/TR/2014/REC-rdf11-concepts-20140225/
 [2] https://tools.ietf.org/html/rfc3986
 [3] https://tools.ietf.org/html/rfc3987
+[4] https://gitlab.cs.fau.de/kissen/iriok