✅ Inherited a class but the compiler does not accept it?

//This is only to make the code more readable
public class Knot{
    public Point Coordinate{get;set;}
    
    public Knot(Point _coordinate){
        Coordinate = _coordinate;
    }

    //This method checks if the current knot is touching the previous knot in the rope in any way in a 3X3 grid
    //If true, the current knot is not supposed to move
    public bool Touch(Knot head){
        for(int scanX = -1; scanX < 2; scanX++){
            for(int scanY = -1; scanY < 2; scanY++){
                Point check = new Point(this.Coordinate.X + scanX, this.Coordinate.Y + scanY);
                if(check == head.Coordinate) return true;
            }
        }
        return false;
    }
}

public class Head : Knot{

    void moveHead(string direction){
        //move head one step at a time
        if(direction is "U") Coordinate.X--;
        if(direction is "D") Coordinate.X++;
        if(direction is "L") Coordinate.Y--;
        if(direction is "R") Coordinate.Y++;
    }
}