# Cross-ORU Contingent Blocks

By [fireballgg.eth](https://paragraph.com/@fireballgg) · 2023-03-21

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Instant bridging for rollups, at the cost of 30% of your soul High-level An ORU block goes through an interactive verification game (“IVG”). This game eventually outputs true or false, after a time period. Contingent blocks add a second validity condition to a Rollup block: the validity of 1 or more other blocks from other rollups. This allows immediate reads of the remote rollup’s state, regardless of whether that rollup’s waiting period has elapsed, because if the state being read reverts, the state reading it must ALSO revert. Structure When sequencing, the sequencer chooses a parent to build upon, and applies state transitions to create a new root. Each child is naturally predicated on the parent. If the parent reverts, the child will too. We generalize this concept to allow the sequencer to also include “parent” roots from other rollups, so long as the validity of that rollup can be verified on the L1. The sequencer chooses undisputed, but pending, roots from other running rollups, and commits them. We call these “predicate roots” because the validity of the new commitment is predicated upon them. We say that a block is “contingent” on its predicate roots. At any time, anyone may notify the Rollup contract that a predicate root does not exist, or has reverted, and cause any contingent root to be invalidated.

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*Originally published on [fireballgg.eth](https://paragraph.com/@fireballgg/cross-oru-contingent-blocks)*