a strange thing about attribute in type inference(whit example)

When I tried to go-through the FS document,a strange occured. What I used was founded in UseCase Doc.:
<book year={$b/@year}>...</book>
As the FS said,this element constructor should be normalized into computed element construtor.So,it should be rewriten like this:
element book{
   attribute year {$b/@year},
   ...
}
I focused this line:attribute year {$b/@year}.
As the rule says:
/////////////////////////////////////////////////////////////////
statEnvs |- expand(QName) = qname   
statEnvs |- ExprSequence : Type1   
Type1 <: xs:AnySimpleType
---------------------------------  
statEnvs |- attribute QName { ExprSequence } : attribute qname { Type1 }   
                   
                 +++ RULE 1+++
/////////////////////////////////////////////////////////////////
The ExprSequence is "$b/@year" and the QName is year.
I had set a statEnvs that $b has the type:
element book{
  attribute year {xsd:integer},
  ...
}
After some caculate(do as the FS told me),the type of "$b/@year" is :
attribute year{ xsd:integer}

So,Type1 in RULE1 is :
Type1=attribute year{ xsd:integer}

Using all these in RULE1,I either got the result:
attribute year { attribute year {xsd:integer} }
or the RULE1 must not be used because Type1 was not the subtype of xs:AnySimpleType(how should i do in this case?).

The wannted result is:
attribute year { xsd:integer}

Here the wrong was!

Perhaps we need another rule to solve this problem.
May I'm wrong since I only read the new FS only one time.But i will be appreciated if someone can explain this strange thing.
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