Why GDP positive growth does not decrease inflation?
GDP growth would lead to deflation if the money supply remained unchanged. The government usually increases money supply as the economy grows to avoid deflation. Controlling money supply is not an easy task though because the economy responds with lag to every policy decision. But ideally, the government aims at keeping inflation low (1-4%) and avoiding deflation. Zero inflation is also undesirable because if you know your money will be worth just as much a year from now, you have less incentive to invest.