Pupils clean grave stones of victims of the Nazis at a cemetery in Berlin, Germany, September 8, 2017. Picture taken September 8, 2017. REUTERS/Hannibal Hanschke

Pupils clean grave stones of victims of the Nazis at a cemetery in Berlin, Germany, September 8, 2017. Picture taken September 8, 2017. REUTERS/Hannibal Hanschke

Pupils clean grave stones of victims of the Nazis at a cemetery in Berlin, Germany, September 8, 2017. Picture taken September 8, 2017. REUTERS/Hannibal Hanschke

Pupils clean grave stones of victims of the Nazis at a cemetery in Berlin, Germany, September 8, 2017. Picture taken September 8, 2017. REUTERS/Hannibal Hanschke

The Big Ben clocktower and a statue of former British Prime Minister Winston Churchill are silhouetted against the morning sky in central London, Britain May 7, 2015. REUTERS/Stefan Wermuth

Leader of the United Kingdom Independence Party Nigel Farage arrives to launch his party's EU referendum tour bus in London, Britain May 20, 2016. REUTERS/Neil Hall

The Big Ben clocktower and a statue of former British Prime Minister Winston Churchill are silhouetted against the morning sky in central London, Britain May 7, 2015. REUTERS/Stefan Wermuth

Leader of the United Kingdom Independence Party (UKIP) Nigel Farage speaks at pro Brexit event in London, Britain June 3, 2016. REUTERS/Neil Hall

Leader of the United Kingdom Independence Party (UKIP) Nigel Farage speaks at pro Brexit event in London, Britain June 3, 2016. REUTERS/Neil Hall

Leader of the United Kingdom Independence Party (UKIP) Nigel Farage arrives to speak at pro Brexit event in London, Britain June 3, 2016. REUTERS/Neil Hall

Leader of the United Kingdom Independence Party (UKIP) Nigel Farage speaks at pro Brexit event in London, Britain June 3, 2016. REUTERS/Neil Hall

Leader of the United Kingdom Independence Party (UKIP) Nigel Farage holds his passport as he speaks at pro Brexit event in London, Britain June 3, 2016. REUTERS/Neil Hall

Leader of the United Kingdom Independence Party (UKIP) Nigel Farage speaks at pro Brexit event in London, Britain June 3, 2016. REUTERS/Neil Hall

Leader of the United Kingdom Independence Party (UKIP) Nigel Farage speaks at pro Brexit event in London, Britain June 3, 2016. REUTERS/Neil Hall

Leader of the United Kingdom Independence Party (UKIP) Nigel Farage speaks at pro Brexit event in London, Britain June 3, 2016. REUTERS/Neil Hall

Leader of the United Kingdom Independence Party (UKIP) Nigel Farage holds his passport at pro Brexit event in London, Britain June 3, 2016. REUTERS/Neil Hall

Leader of the United Kingdom Independence Party (UKIP) Nigel Farage holds his passport as he speaks at pro Brexit event in London, Britain June 3, 2016. REUTERS/Neil Hall

Leader of the United Kingdom Independence Party (UKIP) Nigel Farage speaks at pro Brexit event in London, Britain June 3, 2016. REUTERS/Neil Hall

Leader of the United Kingdom Independence Party (UKIP) Nigel Farage speaks at pro Brexit event in London, Britain June 3, 2016. REUTERS/Neil Hall

Leader of the United Kingdom Independence Party (UKIP) Nigel Farage speaks at pro Brexit event in London, Britain June 3, 2016. REUTERS/Neil Hall

Leader of the United Kingdom Independence Party (UKIP) Nigel Farage wears cuff-links shaped into British RAF bi-planes as he speaks at pro-Brexit event in London, Britain June 3, 2016. REUTERS/Neil Hall

Leader of the United Kingdom Independence Party (UKIP) Nigel Farage speaks at pro Brexit event in London, Britain June 3, 2016. REUTERS/Neil Hall

USS Arizona survivor Lou Conter salutes the names of his fallen shipmates on the "Remembrance Wall' aboard the USS Arizona memorial during ceremonies commemorating the 74th anniversary of the attack on Pearl Harbor at Kilo Pier on Joint Base Pearl Harbor - Hickam in Honolulu, Hawaii December 7, 2015. REUTERS/Hugh Gentry

Pearl Harbor survivors (L to R) Aaron Chabin, Clark Simmons and Armando Gallela talk to media before a ceremony on the USS Intrepid Museum to commemorate the 74th anniversary of the surprise attack on Pearl Harbor, in New York December 7, 2015. REUTERS/Lucas Jackson

Pearl Harbor survivor Clark Simmons smiles before a ceremony on the USS Intrepid Museum to commemorate the 74th anniversary of the surprise attack on Pearl Harbor, in New York December 7, 2015. REUTERS/Lucas Jackson

Pearl Harbor survivor Armando Gallela smiles before a ceremony on the USS Intrepid Museum to commemorate the 74th anniversary of the surprise attack on Pearl Harbor, in New York December 7, 2015. REUTERS/Lucas Jackson

Pearl Harbor survivor Aaron Chabin smiles before a ceremony on the USS Intrepid Museum to commemorate the 74th anniversary of the surprise attack on Pearl Harbor, in New York December 7, 2015. REUTERS/Lucas Jackson

Pearl Harbor survivors Aaron Chabin (L) and Clark Simmons talk before a ceremony on the Intrepid Sea, Air, & Space Museum to commemorate the 74th anniversary of the surprise attack on Pearl Harbor, in New York December 7, 2015. REUTERS/Lucas Jackson

Pearl Harbor survivors (L to R) Armando Gallela, Aaron Chabin, and Clark Simmons smile for friends and family after a ceremony on the Intrepid Sea, Air, & Space Museum to commemorate the 74th anniversary of the surprise attack on Pearl Harbor, in New York December 7, 2015. REUTERS/Lucas Jackson

Pearl Harbor survivors (L to R) Armando Gallela, Clark Simmons, and Aaron Chabin salute during a singing of the Star Spangled Banner during a ceremony on the Intrepid Sea, Air, & Space Museum to commemorate the 74th anniversary of the surprise attack on Pearl Harbor, in New York December 7, 2015. REUTERS/Lucas Jackson

Pearl Harbor survivors (L to R) Armando Gallela, Clark Simmons, and Aaron Chabin wait for a ceremony to start on the Intrepid Sea, Air, & Space Museum to commemorate the 74th anniversary of the surprise attack on Pearl Harbor, in New York December 7, 2015. REUTERS/Lucas Jackson

Pearl Harbor survivors (L to R) Armando Gallela, Clark Simmons, and Aaron Chabin wait for a commemorative ceremony to start on the Intrepid Sea, Air, & Space Museum to commemorate the 74th anniversary of the surprise attack on Pearl Harbor, in New York December 7, 2015. REUTERS/Lucas Jackson

Pearl Harbor survivors (L to R) Armando Gallela, Clark Simmons, and Aaron Chabin watch after tossing a commemorative wreath off the fantail of the USS Intrepid Museum into New York Harbor to commemorate the 74th anniversary of the surprise attack on Pearl Harbor December 7, 2015. REUTERS/Lucas Jackson

Pearl Harbor survivors (L to R) Clark Simmons, Armando Gallela, and Aaron Chabin prepare to toss a commemorative wreath off the fantail of the the USS Intrepid Museum into New York Harbor to commemorate the 74th anniversary of the surprise attack on Pearl Harbor December 7, 2015. REUTERS/Lucas Jackson

Pearl Harbor survivors (L to R) Clark Simmons, Armando Gallela, and Aaron Chabin prepare to toss a commemorative wreath off the fantail of the USS Intrepid into New York Harbor, to commemorate the 74th anniversary of the attack on Pearl Harbor December 7, 2015. REUTERS/Lucas Jackson

Pearl Harbor survivors (L to R) Armando Gallela, Clark Simmons, and Aaron Chabin toss a commemorative wreath off the fantail of the USS Intrepid into New York Harbor, to commemorate the 74th anniversary of the attack on Pearl Harbor December 7, 2015. REUTERS/Lucas Jackson