Downgrading Skills

/// <summary>
/// Determines if the first skill is parented by the second
/// </summary>
/// <param name="child"></param>
/// <param name="potentialParent"></param>
/// <returns></returns>
public bool IsSkillDescended(SkillInfo child, SkillInfo potentialParent)
{
    //require skills to belong here
    if (child == null || potentialParent == null || !Talents.Contains(child) || !Talents.Contains(potentialParent)) return false;
    if (child == potentialParent) return false;

    SkillInfo s = child;
    while (s.prerequisite != null && s.prerequisite != potentialParent) s = s.prerequisite;
    return s.prerequisite == potentialParent;
}

/// <summary>
/// Attempts to lower the level of a skill.
/// Will fail if the skill cannot be lowered validly.
/// </summary>
/// <param name="skill"></param>
/// <returns></returns>
public bool CanDowngradeSkill(SkillInfo skill)
{
    if (skill.CurLevel <= 0) return false;

    //make sure the integrity will be intact
    int specTreeSP = 0;
    foreach (SkillInfo s in Talents)
    {
        if (!IsSkillDescended(s, skill)) specCost += (int)s.totalCost[s.CurLevel];
    }
    //now remove the final level cost
    specTreeSP -= (int)skill.cost[skill.CurLevel];

    foreach (SkillInfo s in Talents.Where((SkillInfo x) => x.CurLevel > 0))
    {
        //make sure that we can still afford this skill
        //and we won't get a broken level
        if (s.spRequirement > specTreeSP
        || (s.prerequisite == skill && skill.CurLevel == 1))
            return false;
    }

    //it's a valid downgrade
    return true;
}