The problem as economics states it
Money performs three functions — medium of exchange, store of value, unit of account — and every monetary system in history has had to trade them off against one another. The Mundell-Fleming trilemma states one form of the constraint: no jurisdiction can simultaneously maintain a fixed exchange rate, free capital movement and independent monetary policy. Keynes proposed the Bancor at Bretton Woods precisely to escape the failure mode of a national currency serving as global reserve, and was refused.
Why the substrate made it unsolvable
Every monetary instrument in existence is backed by something narrow: a sovereign's taxing power, a commodity, or a reserve of financial assets held on an identifiable balance sheet. Narrow backing is what forces the trade-offs, because the backing can be exhausted, devalued, expropriated or run upon. Broad backing was unavailable because there was no mechanism to establish a claim against economic activity in general rather than against an entity in particular.
What the paradigm supplies
The Quantum Privacy Liquidity Pool is backed by continuously settled economic activity across the whole Exchange, enforced by protocol rather than held by an institution, and diversified across sectors, geographies and time horizons by construction rather than by selection. It functions simultaneously as medium of exchange, store of value and coordination layer, and can clear, collateralize, settle and barter across any tokenizable asset, service or outcome. Universal Liquidity resolves the Mundell-Fleming constraint not by choosing differently among the three but by removing the condition that forced the choice.
The Bancor was the right instrument and had no substrate to run on. This is a category-agnostic backing pool of the kind Keynes described, and its availability is a consequence of settlement being universal and non-bypassable rather than of any monetary authority having agreed to anything.
A demonstration that the frictions persist under the mechanism, that credibility still requires cost, or that the mechanism cannot operate at the scale claimed.
Keynes's Bancor · Mundell-Fleming