Formal proof that if a grammar is LR then it isn’t ambiguous

Title says it all. I’m looking for a formal proof that there can’t be two parse trees for a same sentential form if the grammar is LR.

Can you help me?

DreamProxies - Cheapest USA Elite Private Proxies 100 Private Proxies 200 Private Proxies 400 Private Proxies 1000 Private Proxies 2000 Private Proxies ExtraProxies.com - Buy Cheap Private Proxies Buy 50 Private Proxies Buy 100 Private Proxies Buy 200 Private Proxies Buy 500 Private Proxies Buy 1000 Private Proxies Buy 2000 Private Proxies ProxiesLive Proxies-free.com New Proxy Lists Every Day Proxies123