© Licensed to London News Pictures. 24/09/2013. London, UK. The Mayor of Warsaw, Hanna Gronkiewicz-Waltz (L), Boris Johnson, the Mayor of London (2L), Michael Bloomberg, the Mayor of New York (2R) and Matteo Renzi, the Mayor of Florence are seen at the launch of the 2013-2014 Mayor's Challenge at City Hall in London today (24/09/2013). The competition, sponsored by Bloomberg Philanthropies, aims to aid cities to come up with bold solutions to urban challenges  Photo credit: Matt Cetti-Roberts/LNP
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