--- a/src/forward_pdps.rs	Wed Jul 22 16:48:22 2026 -0500
+++ b/src/forward_pdps.rs	Sun Jul 26 17:30:51 2026 -0500
@@ -240,8 +240,7 @@
         // Merge spikes.
         // This crucially expects the merge routine to be stable with respect to spike locations,
         // and not to performing any pruning. That is be to done below simultaneously for γ.
-        let ins = &config.insertion;
-        if ins.merge_now(&state) {
+        config.insertion.if_merge_now(&state, |ins| {
             stats.merged += prox_penalty.merge_spikes(
                 &mut μ,
                 &mut τv,
@@ -252,7 +251,7 @@
                 &reg,
                 Some(|μ̃: &RNDM<N, F>| f.apply(Pair(μ̃, &z))),
             );
-        }
+        });
 
         // Prune spikes with zero weight.
         stats.pruned += prune_with_stats(&mut μ);