public Monoid <B> XSelect <B>(Func <A, B> f, Func <B, A> g)
{
return(Semigroup.XSelect(f, g).Monoid(f(id)));
}
public Reducer <Q, B> XSelect <B>(Func <A, B> f, Func <B, A> g)
{
var t = this;
return(Semigroup.XSelect(f, g).Reducer <Q>(q => f(t.unit(q))));
}