Derives excess demand set based on markets' demand for imports in an
iteration of English auction. Returns a vector with identifiers of
overdemanded importers. Arguments to this function must include a list
of hash maps characterizing demand orrespondence of individual market,
and a hash map with importers' supply constraints.

Checks necessary conditions for prices to be a Walrasian equilibrium
price vector. For each combination of importers, returns a hash map with
aggregate supply/demand balance for goods as values and importers' enumeration
as keys. Arguments to this function must include a list of hash maps
characterizing demand orrespondence of individual market, and a hash map
with importers' supply constraints.