Question: Who did Diederik Boer replace to be behind a Dutch professional footballer?

Context paragraphs:
Diederik Boer: Diederik Boer (born 24 September 1980 in Emmeloord, Netherlands) is a Dutch football player who plays as a goalkeeper.  He currently plays for PEC Zwolle in the Eredivisie.  Boer made his professional debut on 8 March 2003, when FC Zwolle lost to Ajax 5–0.  On 31 August 2014 Boer signed a three-year contract with Ajax to replace the departed Kenneth Vermeer as second keeper behind Jasper Cillessen.

Donny Gorter: Donny Gorter (born 15 June 1988) is a Dutch professional footballer who currently plays as a left back for ADO Den Haag in the Dutch Eredivisie.  He formerly played for NAC Breda, AZ, AaB and Viborg FF.  He is the son of former footballer Edwin Gorter.

Mustafa Saymak: Mustafa Saymak (born 11 February 1993 in Deventer) is a Dutch professional footballer of Turkish descent who currently plays as a Winger for PEC Zwolle in the Dutch Eredivisie.  He has represented both the Turkish Football Federation and Royal Dutch Football Association at various youth levels.

Vito van Crooy: Vito van Crooy (born 29 January 1996 in Venlo) is a Dutch professional footballer who currently plays as a winger, primarily on the left hand side, for VVV-Venlo in the Dutch Eredivisie.  He plays also in the Dutch National Team under 21 and won the Eerste Divisie Young Player of the year in 2016 for his performances for VVV-Venlo.  His brother, Delano van Crooy also plays for VVV-Venlo as a goalkeeper.

Jasper Cillessen: Jacobus Antonius Peter "Jasper" Cillessen (] ; born 22 April 1989) is a Dutch professional footballer who plays as a goalkeeper for Spanish club FC Barcelona and the Netherlands national team.

Bryan Linssen: Bryan Linssen (born 8 October 1990) is a Dutch professional footballer, who currently plays for Vitesse in the Dutch Eredivisie.  He formerly played for Fortuna Sittard, MVV, VVV-Venlo, Heracles Almelo and FC Groningen.  He is the younger brother of professional footballer Edwin Linssen.

Ivar van Dinteren: Ivar van Dinteren (born 3 May 1979) is a former Dutch professional footballer who was last a coach for Dayton Dutch Lions in the USL Professional Division in 2012.

Daryl van Mieghem: Daryl van Mieghem (born 5 December 1989 in Amsterdam) is a Dutch professional footballer who plays as a winger for De Graafschap on loan from Heracles Almelo, in the Dutch Eerste Divisie.  He formerly played professional football for Telstar and Excelsior before signing a new deal with Heracles Almelo.  On 9 August 2013, he made his first goal for Telstar against FC Emmen.

Oussama Idrissi: Oussama Idrissi (born 26 February 1996, in Bergen op Zoom) is a Dutch professional footballer who currently plays as a winger for FC Groningen in the Dutch Eredivisie.  He was born in the Netherlands to parents of Moroccan descent, and has represented the Royal Dutch Football Association at various youth levels.

Sophie de Boer: Sophie de Boer (born 12 December 1990) is a Dutch professional racing cyclist.

Supporting paragraphs: Diederik Boer Jasper Cillessen
Answer: Kenneth Vermeer