Some code for context:

class a
{

}

class b
{
    public a a{get;set;}
    public static implicit operator a(b b)
    {
        return b.a;
    }
}

  a a=null;
  b b=null;
  a = b;

  //compiler: cannot apply operator '==' to operands of type tralala...
  bool c = a == b;

Is it possible to use == operator on different type instances, where one can implicitly convert to another? What did i miss?

Edit:
If types must be the same calling ==, then why

int a=1;
double b=1;
bool c=a==b;

works?