Implementing COGS with multicurrency

[Vladimir Avramenko]

There is perfect explanation for the process with single currency given 
in http://permalink.gmane.org/gmane.comp.gnome.apps.gnucash.user/44097

Could someone please give me the similar scheme for the case of two 
currencies. Namely:
1. Suppose my Company resells air tickets in USD.
2. Company takes a ticket from Vendor (Vendor works with EUR, and the 
ticket costs 100 EUR)
3. Company resells ticket to Customer in USD with rate EUR = 1.3 USD 
plus Company takes an additional Fee 10 USD from Customer
4. Company pays 100 EUR to Vendor with rate EUR=1.4 USD

It is preferable to use Trading account because, according to article 
http://www.mathstat.dal.ca/~selinger/accounting/tutorial.html, it is the 
most correct way to deal with multicurrency.
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Thank you in advance,
Vladimir