# Cheapest-to-deliver (CTD) discount curve II

I have come across the following relationship in a CTD curve bootstrapping routine:

$$\frac{DF_{XXX}^{CSA.EUR}}{DF_{EUR}^{CSA.EUR}} = \frac{DF_{XXX}^{CSA.USD}}{DF_{EUR}^{CSA.USD}}$$

where $$XXX$$ is a generic currency (e.g. CAD) and $$DF_{XXX}^{CSA.EUR}$$ denotes a discount factor collateralized in EUR, etc.

Would some be able to explain why(and under what conditions) is this true?