//c# does not allow flexible overload of <<
/// <summary>
/// Inverse implication operator on two Bdds
/// </summary>
/// <param name="l">Left Bdd</param>
/// <param name="r">Right Bdd</param>
/// <returns>Resulting Bdd</returns>
public static Bdd operator <=(Bdd l, Bdd r)
{
return(Kernel.InvImp(l, r));
}