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A banner showing Turkish Prime Minister Binali Yildirim advertising for the 'yes' vote in the April 16 referendum in Istanbul, Turkey, on 13 April 2017. The Turkish public will vote on April 16, 2017 on whether to change the current parliamentary system into an executive presidency. (Photo by Erhan Demirtas/NurPhoto via Getty Images)

A banner showing Turkish Prime Minister Binali Yildirim advertising for the 'yes' vote in the April 16 referendum in Istanbul, Turkey, on 13 April 2017. The Turkish public will vote on April 16, 2017 on whether to change the current parliamentary system into an executive presidency. (Photo by Erhan Demirtas/NurPhoto via Getty Images)

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People wave "YES" (Evet) flags in Istanbul, Turkey, on 13 April 2017. The Turkish public will vote on April 16, 2017 on whether to change the current parliamentary system into an executive presidency. (Photo by Erhan Demirtas/NurPhoto via Getty Images)

People wave "YES" (Evet) flags  in Istanbul, Turkey, on 13 April 2017. The Turkish public will vote on April 16, 2017 on whether to change the current parliamentary system into an executive presidency. (Photo by Erhan Demirtas/NurPhoto via Getty Images)

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A banner showing Turkish Prime Minister Binali Yildirim advertising for the 'yes' vote in the April 16 referendum in Istanbul, Turkey, on 14 April 2017. The Turkish public will vote on April 16, 2017 on whether to change the current parliamentary system into an executive presidency. (Photo by Erhan Demirtas/NurPhoto via Getty Images)

A banner showing Turkish Prime Minister Binali Yildirim advertising for the 'yes' vote in the April 16 referendum in Istanbul, Turkey, on 14 April 2017. The Turkish public will vote on April 16, 2017 on whether to change the current parliamentary system into an executive presidency. (Photo by Erhan Demirtas/NurPhoto via Getty Images)

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A women walk to Eminonu square on March 18th 2017 in Istanbul, Turkey. (Photo by Emrah Oprukcu/NurPhoto via Getty Images)

A women walk to Eminonu square on March 18th 2017 in Istanbul, Turkey. (Photo by Emrah Oprukcu/NurPhoto via Getty Images)

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People wave 'YES' banners and Turkish national flags on April 8, 2017 during a campaign rally for the 'yes' vote in a constitutional referendum in Istanbul. On April 16, 2017, the Turkish public will vote on whether to change the current parliamentary system into an executive presidency. / AFP PHOTO / OZAN KOSE (Photo credit should read OZAN KOSE/AFP/Getty Images)

People wave 'YES' banners and Turkish national flags on April 8, 2017 during a campaign rally for the 'yes' vote in a constitutional referendum in Istanbul.
On April 16, 2017, the Turkish public will vote on whether to change the current parliamentary system into an executive presidency.  / AFP PHOTO / OZAN KOSE        (Photo credit should read OZAN KOSE/AFP/Getty Images)