RIO DE JANEIRO:G20 leaders gather in Brazil on Monday for a G20 summit set to be dominated by differences over wars in the Middle East and Ukraine, and implications of Donald Trump’s White House return.Security considerations — always high at such meetings — were elevated further after a failed bomb attack late Wednesday outside Brazil’s Supreme Court in Brasilia.Police were probing the two blasts as a possible “terrorist act” committed by a Brazilian perpetrator, whose death was the sole casualty.