user2540: I read somewhere that there is no risk of forks because ADA has a built in way of deciding who gets to propose the next block if multiple stakers get selected in 1 round:
The one who rolls the lowest number that satisfies the requirement gets to propose a block.
But if you control a lot of stake, couldn't it happen that you get selected twice? In that case you can first publish the first VRF, purchase a product in that block, then reveal your lower VRF and make a fork where you keep your funds (ie a double spend).
Anything that stops this?

user50: Nothing at stake usually means, a block producer may produce multiple blocks simultaneously and either send those to different nodes, or keep some for later in order to perform a long-range attack.
Now in Ouroboros PoS the slot leaders are pre-compiled and determined by VRF mechanism. Each participating node can easily verify if the produced block was actually built by a valid slot leader.
Also in Cardano's PoS the node does not submit/broadcast his new block, but just announce his current block-height. The remote node then decides if he want/need to fetch this block or not (i.e. a pull mechanism instead of a broadcast/push mechanism)
Also micro forks based on multiple valid blocks for the same slot - which can even happen naturally without bad intentions, based on the random slot leader election - are quickly solved by always choosing the block with the lowest VRF dice result.

2540: <p>I read somewhere that there is no risk of forks because ADA has a built in way of deciding who gets to propose the next block if multiple stakers get selected in 1 round:</p>
<p>The one who rolls the <em>lowest</em> number that satisfies the requirement gets to propose a block.</p>
<p>But if you control a lot of stake, couldn't it happen that you get selected twice? In that case you can first publish the first VRF, purchase a product in that block, then reveal your <em>lower</em> VRF and make a fork where you keep your funds (ie a double spend).</p>
<p>Anything that stops this?</p>
 50: <p>Nothing at stake usually means, a block producer may produce multiple blocks simultaneously and either send those to different nodes, or keep some for later in order to perform a long-range attack.</p>
<p>Now in Ouroboros PoS the slot leaders are pre-compiled and determined by VRF mechanism. Each participating node can easily verify if the produced block was actually built by a valid slot leader.</p>
<p>Also in Cardano's PoS the node does not submit/broadcast his new block, but just announce his current block-height. The remote node then decides if he want/need to fetch this block or not (i.e. a pull mechanism instead of a broadcast/push mechanism)</p>
<p>Also micro forks based on multiple valid blocks for the same slot - which can even happen naturally without bad intentions, based on the random slot leader election - are quickly solved by always choosing the block with the lowest VRF dice result.</p>
