抄録
Let {H^∞ } be an abstract Hardy space associated with a uniform algebra. Denoting by (f) the coset in {({L^∞ }) - 1}/{({H^∞ }) - 1} of an f in {({L^∞ }) - 1}, define \left// {(f)} \
ight// = \inf { {\left// g \
ight//_∞ }{\left// {{g - 1}} \
ight//_∞ };g \in (f)} and { \left// {(f)} \
ight//;(f) \in {({L^∞ }) - 1}/{({H^∞ }) - 1}} . If {γ _0} is finite, we show that the norms of Hankel operators are equivalent to the dual norms of {H^1} or the distances of the symbols of Hankel operators from {H^∞ }. If {H^∞ } is the algebra of bounded analytic functions on a multiply connected domain, then we show that {γ _0} is finite and we determine the essential norms of Hankel operators.
