diff --git a/R/Koenigsberg.R b/R/Koenigsberg.R
index 5415e47..8dde8c4 100644
--- a/R/Koenigsberg.R
+++ b/R/Koenigsberg.R
@@ -32,7 +32,9 @@
 #'   from his paper.
 #'
 #'   This dataset is in the public domain.
+#' @references Leonhard Euler, “Solutio problematis ad geometriam situs pertinensis”
+#' Commentarii Academiae Scientarum Imperialis Petropolitanae, 8 (1736), 128–140 + Plate VIII.
 #' @source Wikipedia,
-#'   <http://de.wikipedia.org/wiki/K%C3%B6nigsberger_Br%C3%BCcken>
+#'   <https://en.wikipedia.org/wiki/Seven_Bridges_of_K%C3%B6nigsberg>
 #' @keywords datasets
 NULL
diff --git a/man/Koenigsberg.Rd b/man/Koenigsberg.Rd
index 23f6d9b..680b522 100644
--- a/man/Koenigsberg.Rd
+++ b/man/Koenigsberg.Rd
@@ -15,7 +15,7 @@ This dataset is in the public domain.
 }
 \source{
 Wikipedia,
-\url{http://de.wikipedia.org/wiki/K\%C3\%B6nigsberger_Br\%C3\%BCcken}
+\url{https://en.wikipedia.org/wiki/Seven_Bridges_of_K\%C3\%B6nigsberg}
 }
 \usage{
 Koenigsberg
@@ -37,4 +37,8 @@ then turn around and later cross the other half from the other side).
 
 Euler proved that the problem has no solution.
 }
+\references{
+Leonhard Euler, “Solutio problematis ad geometriam situs pertinensis”
+Commentarii Academiae Scientarum Imperialis Petropolitanae, 8 (1736), 128–140 + Plate VIII.
+}
 \keyword{datasets}