> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cast.digitalfinancehq.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Deterministic commerce

> Why reconciliation should not exist.

Reconciliation is one of the largest standing costs in commercial finance. It exists because two parties keep independent records of the same transaction. CAST's claim is that this cost is not inherent to commerce — it is an artifact of a design choice, and a different design removes it.

## Why reconciliation exists

When a buyer and a vendor each maintain their own record of a transaction, those records are produced separately, from separate inputs, by separate systems. When they happen to agree, everyone assumes correctness. When they disagree, both sides reconstruct the truth from email threads and PDF attachments — slow, expensive, and often inconclusive.

## Why reconciliation is waste

The work of reconciliation produces no new value. It does not improve the transaction; it merely recovers agreement that should have existed from the start. It is pure overhead imposed by the absence of a shared record.

## Event-sourced finance

In CAST, the append-only event log is the system of record, and every other view is a projection of it. There is one record, co-authored, not two records to compare.

<Note>
  Deterministic state machines: the same events, applied by different parties, always produce identical outputs. Agreement is guaranteed by construction, not recovered by reconciliation.
</Note>

## Deterministic settlement

Because settlement is derived from the same co-authored events both parties hold, there is no point at which the two sides can drift. The posting on the buyer's side and the receivable on the vendor's side are projections of one shared truth.

<Card title="From systems of record to systems of coordination" icon="arrow-right-arrow-left" href="/start-here/record-to-coordination">
  The conceptual shift this rests on.
</Card>