- Rigard, Righard,
Reghard Danish: Rikard, Ryker, Richard,
Richardt Dutch:
Rijkert, Rikkert, Ryker, Rigard, Richart, Richard,
Richardt Gothic: RekkareÞ (Reccared)...
- Iwt.be.
Archived from the
original on 2011-09-29.
Retrieved 2012-09-16.
Rijkert Knoppers (25
April 2010). "Universiteit Gent
ontwerpt golfenergiecentrale"...
- to
Schiphol in the sea] (in Dutch). Volkskrant.
Retrieved 2010-04-15.
Rijkert Knoppers (16
January 1999). "Dertig
kilometer electriciteit" [Thirty kilometers...