Compiler can't resolve generic types?

Question

Is there any difference between:

public interface IPathfinding<T> where T : IPathfindingEntity
{
    IEnumerable<T> GetShortestPath(IPathfindingUtils<IGraphNode<T>> utils);
}

and:

public interface IPathfinding<T> where T : IPathfindingEntity
{
    IEnumerable<T> GetShortestPath(IPathfindingUtils<IGraphNode<IPathfindingEntity>> utils);
}

I'm scratching my head as intuitively it doesn't seem like there should be yet I am receiving compiler error in example #1:

IGraphNode<T> cannot be used as parameter T in the generic type IPathfindingUtils<T>. There is no implicit reference conversion from IGraphNode<T> to IGraphNode<IPathfindingEntity>

I haven't changed the definition of IGraphNode<T> or IPathfindingUtils<T> between trying to compile the 2 examples, here are the definitions for those interfaces:

public interface IPathfindingUtils<T> where T : IGraphNode<IPathfindingEntity>
{
    float Heuristic(T from, T to);
    IEnumerable<T> CreatePath(T from);
}

public interface IGraphNode<T> : INode<T>, IComparable<IGraphNode<T>> where T : IComparable<T>
{
    IList<float> Costs { get; }
}

Answer 1

IGraphNode requires T to be an IComparable.

So you will want your code to be the following:

 public interface IPathfinding<T> where T : IPathfindingEntity, IComparable
 {
     IEnumerable<T> GetShortestPath(IPathfindingUtils<IGraphNode<T>> utils);
 }

Answer 2

Never mind, I've rubber ducked myself and realized what the problem is.

For posterity:

In example #1, the constraint on T is IPathfindingEntity . IGraphNode<T> is not constrained against IPathfindingEntity and so IPathfindingUtils<IGraphNode<T>> utils is not valid since T in this case is IPathfindingEntity and that would break liskov substitution against IGraphNode<T> constraint which is not fullfilled!

So solution is to just make IPathfinding specifiy IGraphNode constraint in method definition as per example #2?