IRA Cross Pollination?

[Ian Jaeger]

So one of the things we can't do with an IRA is self manage your property. But you can invest in someone else's property.

So what are the rules if two friends who both have $ locked up in their IRA's would fund each others rental properties. For example I invest in a buddy $50k from my IRA, and he invests $50k from his to me?

Kinda curious.