From 6dacf74645d7fb401271ea82223859fe9b79bdff Mon Sep 17 00:00:00 2001
From: cyphersnake <cyphersnake@pm.me>
Date: Thu, 6 Feb 2025 17:45:00 +0100
Subject: [PATCH] fix(ivc): sangria ro consistency

**Motivation**
The bug was that with empty step circuit instances within sangria::IVC there was no absorption of formal zero

**Overview**
N/A
---
 src/ivc/sangria/fold_relaxed_plonk_instance_chip.rs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/ivc/sangria/fold_relaxed_plonk_instance_chip.rs b/src/ivc/sangria/fold_relaxed_plonk_instance_chip.rs
index 19cab9d3..0614660a 100644
--- a/src/ivc/sangria/fold_relaxed_plonk_instance_chip.rs
+++ b/src/ivc/sangria/fold_relaxed_plonk_instance_chip.rs
@@ -898,7 +898,12 @@ where
 
         let assigned_step_circuit_instances =
             match self.relaxed.step_circuit_instances_hash_accumulator {
-                SCInstancesHashAcc::None => SCInstancesHashAcc::None,
+                SCInstancesHashAcc::None => {
+                    assign_and_absorb_diff_field!(&C::Base::ZERO, || {
+                        "empty step_circuit_instances"
+                    })?;
+                    SCInstancesHashAcc::None
+                }
                 SCInstancesHashAcc::Hash(hash) => {
                     SCInstancesHashAcc::Hash(assign_and_absorb_diff_field!(&hash, || {
                         "step_circuit_instances"