fluent nhibernate mapping for combination of table per subclass and single table with discriminator

Question

I am new to fluent nhibernate. I have the following combination of table per subclass and single table with discriminator per subclass structure. Will appreciate any help in mapping this with fluent - specially with automapping:

enum type {a, b, c, d}

Class pool
{
int id;
IList<Class1> aVals;

IList<Class1> bVals;

IList<Class2> cVals;

IList<Class3> dVals;
}

Class Class1
{
int ID;
Type discriminator;
string value;
}


class Class2 : Class1 //This is only for type c
{
string SomeExtraProperty;
}

Class Class3 : class1 //This is only for type d
{
string AnotherExtraProperty;
}

DB tables: Table Pool ( id int identity, name varchar(50) )

table Class1( id int identity, pool_id int references(pool.id), value varchar(50) )

table Class2 ( id int identity, Class1_id int references(Class1.id), SomeProperty varchar(50) )

table Class2 ( id int identity, Class1_id int references(Class1.id), anotherProperty varchar(50) )