public CalcRelation AddRelationFrom(CalcCell other, CalcChain chain)
{
if (_relationsFrom.ContainsKey(other.Id)) return _relationsFrom[other.Id];
var rel = new CalcRelation { CalcCellId = other.Id, CalcChainId = chain.Id };
_relationsFrom.Add(other.Id, rel);
return rel;
}