private string _generalLogicResult(UBasCov2 BasCov)
        {
            try{
                var BaseSetLst  = BasCov.BaseSetLst;        //BaseSet  list
                var CoverSetLst = BasCov.CoverSetLst;       //CoverSet list

                Bit81 Q = new Bit81();
                foreach (var P in CoverSetLst)
                {
                    Q |= P.rcnBit.CompressToHitCells();
                }
                foreach (var UC in Q.IEGetRC().Select(rc => pBDL[rc]))
                {
                    UC.SetCellBgColor(SolBkCr2);
                }

                for (int rc = 0; rc < 81; rc++)
                {
                    int noB = BasCov.HB981.IsHit(rc);
                    if (noB > 0)
                    {
                        pBDL[rc].SetNoBBgColor(noB, AttCr, SolBkCr);
                    }
                }

                string msg  = "\r     BaseSet: ";
                string msgB = BaseSetLst.Aggregate("", (Q, P) => Q + $" {P.ToAppearance()}");
                msg += msgB.ToString_SameHouseComp1();

                msg += "\r    CoverSet: ";
                string msgC = CoverSetLst.Aggregate("", (Q, P) => Q + $" {P.ToAppearance()}");
                msg += msgC.ToString_SameHouseComp1();

                string st = $"GeneralLogic size:{BasCov.sz} rank:{BasCov.rnk}";
                Result     = st;
                msg       += $"\rChkBas:{ChkBas4}/{ChkBas1}  ChkCov:{ChkCov2}/{ChkCov1}";
                ResultLong = st + "\r " + msg;
                return(st + "\r" + msg);
            }
            catch (Exception ex) { WriteLine(ex.Message + "\r" + ex.StackTrace); }
            return("");
        }
        public IEnumerable <UBasCov2> IEGet_BaseSet(int sz, int rnk)        //### BaseSet generator
        {
            if (GLK_UList_All.Count < sz * 2 + rnk)
            {
                yield break;
            }

            BSstatus2 = new BaseSet_Status2(sz, rnk);

            //Marking method
            // #1:Focus on the link(LK0) and follow the connecting links. A link of size(sz) is a candidate for BaseSet/CoverSet.
            //    (This alone won't make it faster.)
            // #2:Select BaseSet from the candidates and check suitability.
            //    Excludes generation G1 links.
            // #3:Also select the CoverSet from the candidates. At least common elements with baseset are required.
            //    Light selection and aptitude testing.
            //    Efficient evaluation of aptitude of baseSet is important.
            // #4:If there is no solution for the candidate starting from LK0, record LK0 in the invalid list.
            // #2':Select BaseSet from the candidates, exclude links in the invalid list.

            Bit324 invalidLink = new Bit324();

            foreach (var LK0 in GLK_UList_All)      //#1 LK0:First link
            {
                _chkX1 = false; _chkX2 = false;

                //    if( SDK_Ctrl.UGPMan.stageNo>=12 && sz>=3 ){//&& rnk==1){
                //        _chkX1=false; _chkX2=true;
                //        if(LK0.ToAppearance()=="r4#2"){
                //            WriteLine($"--->{LK0.ToAppearance()}");
                //            _chkX1=false; _chkX2=true;
                //        }
                //    }
                if (_chkX1)
                {
                    WriteLine($"\r-1- baseset sz:{sz} rnk:{rnk}  first:{LK0} -");
                }

                GLK_UList_Marked.Clear();
                QueueGlk.Clear();
                rcnGenNo         = new int[9, 81];      //### gen ###
                BasCovCandidates = new Bit324();

                #region ----- marking for LK0 -------------------------
                BasCovCandidates.BPSet(LK0.IDsq);             //1)BC_Set 候補のリスト  ## 初のリンク(LK0)の登録
                LK0._gen = 1;
                foreach (var NDx in LK0.ConnectLinks)         //LK0の他端ノードNDx に着目
                {
                    var(rc, no)      = (NDx >> 4, NDx & 0xF); // (rc,no) <-- NDx
                    rcnGenNo[no, rc] = 1;                     //### gen ###      //NDXの世代<-1    set rcnGenNo
                    QueueGlk.Enqueue(NDx);                    //Enqueue(ND1)
                    if (_chkX1)
                    {
                        WriteLine($"@{_jkc_++}      -1.5- Enqueue {rc.ToRCString()}#{no+1}");
                    }
                }

                //==== sz>=2 ====
                while (QueueGlk.Count > 0)
                {
                    var ND2 = QueueGlk.Dequeue();
                    var(rc, no) = (ND2 >> 4, ND2 & 0xF);
                    int gen = rcnGenNo[no, rc];            //### gen ###
                    if (_chkX1)
                    {
                        WriteLine($"@{_jkc_++}  -2- Dequeue {rc.ToRCString()}#{no+1}-G{gen}");
                    }

                    if (gen > sz)
                    {
                        continue;
                    }
                    foreach (var LKpair in GLK_connection[rc, no])
                    {
                        var(no2, rc2) = (LKpair.no2, LKpair.rc2);
                        var         gen2 = rcnGenNo[no2, rc2]; //### gen ###
                        UGLink_unit LKx  = LKpair.objUGL;
                        LKx._gen = gen;
                        bool hit = BasCovCandidates.IsHit(LKx.IDsq);
                        BasCovCandidates.BPSet(LKx.IDsq);   //1)BC_Set 候補のリスト ビット表現で重複を回避
                        if (_chkX1)
                        {
                            string st3 = $"@{_jkc_++}      -2.5- Link set {LKx} {(hit? "---": "New")}";
                            WriteLine(st3);
                        }

                        if (gen2 == 0)
                        {
                            rcnGenNo[no2, rc2] = gen + 1;  //### gen ###
                            if (gen < sz)
                            {
                                QueueGlk.Enqueue(LKpair.rcno);
                                if (_chkX1)
                                {
                                    string st3 = $"@{_jkc_++}         -3- Enqueue {rc2.ToRCString()}#{no2+1}-G{gen+1}";
                                    st3 += "   " + LKx.ToString();
                                    WriteLine(st3);
                                }
                            }
                        }
                    }
                }

                GLK_UList_Marked.Add(LK0);                  //First is LK0.
                BasCovCandidates.BPReset(LK0.IDsq);         //reset LK0.
                foreach (var LX in BasCovCandidates.IEGet_Index().Select(kx => GLK_UList_All[kx]))
                {
                    GLK_UList_Marked.Add(LX);
                }
                if (_chkX2)
                {
                    string stBC = $"\r@{_jkc_++} BasCovCandidates({GLK_UList_Marked.Count}) :";
                    GLK_UList_Marked.ForEach(LK => stBC += $" {LK.ToAppearance(Gen:true)}");       //#### debug print
                    WriteLine(stBC);
                }
                if (GLK_UList_Marked.Count < sz)
                {
                    continue;
                }
                #endregion ----- marking -------------------------

                #region ----- selecte -------------------------
                var         GLK_UList_Sel = new List <UGLink_unit>();
                Combination cmbBas = new Combination(GLK_UList_Marked.Count, sz);
                string      st, stw = "";
                int         nxt = int.MaxValue;             //(skip function)
                string      stT = "";
                while (cmbBas.Successor(nxt))
                {
                    nxt = int.MaxValue;
                    if (cmbBas.Index[0] != 0)
                    {
                        continue;                    //"The first link is fixed at 0!"
                    }
                    GeneralLogicGen2.ChkBas0++;      //*****

                    var   usedLKIDsq  = new Bit324();
                    var   BaseSetLst  = new List <UGLink_unit>();
                    var   HB981       = new Bit981(); //BaseSet bitPattern
                    long  RCBN_frameA = 0;
                    int[] RCB_frameB9 = new int[9];
                    foreach (var(kx, elementX) in cmbBas.IEGetIndex2())
                    {
                        nxt = kx;
                        var UGL = GLK_UList_Marked[elementX];
                        if (kx >= 1 && UGL._gen == 1)
                        {
                            goto LnxtCombination;                                   // (#2) excludes generation G1 links.
                        }
                        if (invalidLink.IsHit(UGL.IDsq))
                        {
                            goto LnxtCombination;                                   // (#2')exclude links in the invalid list.
                        }
                        usedLKIDsq.BPSet(UGL.IDsq);
                        BaseSetLst.Add(UGL);
                        foreach (var P in UGL.ConnectLinks)
                        {
                            int no2 = P & 0xF, rc2 = P >> 4;
                            if (HB981.IsHit(no2, rc2))
                            {
                                goto LnxtCombination;                               // BaseSet links do not overlap.
                            }
                            HB981.BPSet(no2, rc2);
                        }
                        long RCBN_frameB = UGL.RCBN_frameB; //bit expression of [ UC.FreeB<<27 | 1<<(UC.b+18)) | 1<<(UC.c+9) | (1<<UC.r) ]
                        int  freebX      = (int)(RCBN_frameB >> 27);
                        foreach (var no in freebX.IEGet_BtoNo())
                        {
                            RCB_frameB9[no] |= (int)(RCBN_frameB & 0x7FFFFFF);
                        }
                        RCBN_frameA |= UGL.RCBN_frameB;    //bit expression of rcb
                        if (kx > 0)
                        {
                            if (!Check_rcbnCondition(sz, rnk, elementX, RCBN_frameA))
                            {
                                goto LnxtCombination;                                                     //(### extremely efficient) ????
                            }
                        }
                    }
                    if (!Check_rcbnCondition(sz, rnk, 0, RCBN_frameA))
                    {
                        goto LnxtCombination;                                              //Evaluate BaseSet pattern. Extremely efficient.
                    }
                    if (sz >= 2)
                    {
                        BSstatus2.Prepare(usedLKIDsq, BaseSetLst, HB981, RCB_frameB9);

                        //check 421 52.1sec
                        //check 124 53.6sec

                        if (!BSstatus2.Check_4())
                        {
                            goto LnxtCombination;                           //Each element of LK0 is associated with the rest of the links.
                        }
                        if (!BSstatus2.Check_2())
                        {
                            goto LnxtCombination;                           //Each cell(A) is in a position to link with other cells.
                        }
                        if (!BSstatus2.Check_1())
                        {
                            goto LnxtCombination;                           //A and B are not linked by other link(C).
                        }
                        //  if( !BSstatus2.Check_3() ) goto LnxtCombination;  //There is a limit to the number of cells that have no links other than BaseSet.
                        //      Check_1 and _3 are almost the same evaluation. Check_3 is a heavy process.

                        //  if( !BSstatus2.Check_5() ) goto LnxtCombination;  //XXX Almost no effect. Check_1-4 has been determined.
                    }
                    var BasCov = new UBasCov2(usedLKIDsq, BaseSetLst, HB981, sz);
                    if (_chkX2)
                    {
                        string st2 = $"\r{_jkc_++} BaseSet:";
                        BaseSetLst.ForEach(P => st2 += " " + P.ToAppearance());
                        //     WriteLine(st2);
                        WriteLine($"Check_5---->{st2}");            //###################
                    }
                    yield return(BasCov);

LnxtCombination:
                    continue;
                }

                //*==*==*==*==*==*==*==*==*==*==*==*==*==*==*==*
                invalidLink.BPSet(LK0.IDsq); //#4:If there is no solution for the candidate starting from LK0, record LK0 in the invalid list.
                //*==*==*==*==*==*==*==*==*==*==*==*==*==*==*==*

                #endregion ----- selecte -------------------------
            }
            yield break;
        }
        //1..4....8.9.1...5.....63.....13.5.79..3...8..76.2.94.....75.....1...6.4.8....4..2

        public IEnumerable <UBasCov2> IEGet_CoverSet(UBasCov2 BasCov, int rnk)           //### CoverSet generator
        {
            if (GLK_UList_All == null)
            {
                yield break;
            }
            int sz = BasCov.sz;

            if (GLK_UList_Marked.Count < sz)
            {
                yield break;
            }

            var BaseSetLst = BasCov.BaseSetLst;
            var usedLKIDsq = BasCov.usedLKIDsq;              //used links
            var HB981      = BasCov.HB981;                   //BaseSet bit expression
            int noBit      = HB981.noBit;                    //bit expression of digits containing cell elements

            var UGLCovCandidates = new List <UGLink_unit>(); // UGLCovCandidates:candidate link

            #region Preparation(Create UGLCovCandidates)
            //Preparation: select candidates for CoverSet.(this process is extremely effective!)
            // 1)First select BaseSet, then select CoverSet to cover.
            // 2)CoverSet requirements:
            //  .Exclude links that do not contain BaseSet elements
            //  .Rank=0 includes two or more elements of BaseSet
            //  .Rank>0 contains one or more elements of BaseSet

            Bit81 Bcmp = HB981.CompressToHitCells();
//x            long  RCBN_frameBex = BaseSetLst.Aggregate((long)0,(p,q)=>p|q.RCBN_frameBex);

            foreach (var P in GLK_UList_Marked)    //Exclude Baseset links
//x                if((RCBN_frameBex&P.RCBN_frameB) == 0) continue;
            {
                if (BaseSetLst.Contains(P))
                {
                    continue;
                }
                if (P.type == 0)          // 0:link
                {
                    if ((noBit & (1 << P.no)) == 0)
                    {
                        continue;                                           //Exclude links with digits not included in BaseSet.
                    }
                    int Bcount = (HB981._BQ[P.no] & P.rcBit81).BitCount();  //Bcount : Number of cells in common with BaseSet.
                    if (Bcount == 0)
                    {
                        continue;                                           //Link without common parts is excluded from candidate links.
                    }
                    if (rnk == 0 && Bcount < 2)
                    {
                        continue;                                           //if rank=0, the CoverSet has two or more common items
                    }
                    UGLCovCandidates.Add(P);
                }

                else                   // 1:cell
                {
                    if (noBit.BitCount() <= 1)
                    {
                        continue;                                           //For links within a cell, the Coverset digits must be 2 or more.
                    }
                    if ((noBit & P.FreeB) == 0)
                    {
                        continue;                                           //Exclude links with digits not included in BaseSet.
                    }
                    int B = noBit & P.FreeB;                                //Common digits of BaseSet and link
                    if (B == 0)
                    {
                        continue;                                           //Link without common parts are excluded from candidate links.
                    }
                    int rc = P.rc;                                          //focused cell

                    int kcc = 0, kccLim = (rnk == 0)? 2:1;
                    foreach (var no in B.IEGet_BtoNo())                     //no:Candidate digit of forcused cell.
                    {
                        if (!HB981._BQ[no].IsHit(rc))
                        {
                            continue;                                       //do not check if BaseSet does not include no.
                        }
                        if (++kcc >= kccLim)
                        {
                            UGLCovCandidates.Add(P); break;
                        }                                                   //number of digits contained in BaseSet satisfies the condition(kccLim).
                    }
                }
            }
            if (_chkX2)
            {
                string st2 = $"{_jkc_++} UGLCovCandidates for CoverSet:";
                st2 = UGLCovCandidates.Aggregate(st2, (p, q) => p + " " + q.ToAppearance());//#### debug print

                WriteLine(st2);
            }
            #endregion Preparation(Create UGLCovCandidates)

            #region CoverSet generator
            if (UGLCovCandidates.Count < sz + rnk)
            {
                yield break;
            }
            Bit981 HC981  = new Bit981();         //CoverSet
            Bit981 Can981 = new Bit981();         //Items that break "Locked"(excludable candidates)

            Combination cmbCvr = new Combination(UGLCovCandidates.Count, sz + rnk);
            int         nxt    = int.MaxValue;
            while (cmbCvr.Successor(nxt))                                               //Combination one-element generator
            {
                ++GeneralLogicGen2.ChkCov1;
                HC981.Clear();
                Array.ForEach(cmbCvr.Index, m => HC981 |= UGLCovCandidates[m].rcnBit);  //CoverSet bit expression

                if (!(HB981 - HC981).IsZero())
                {
                    goto LNextSet;                                                      //BaseSet is covered?
                }
                Bit981 CsubB = HC981 - HB981;                                           //CsubB:excludable candidates
                if (CsubB.IsZero())
                {
                    goto LNextSet;                                                      // is exist?
                }
                var CoverSetLst = new List <UGLink_unit>();
                Array.ForEach(cmbCvr.Index, m => CoverSetLst.Add(UGLCovCandidates[m])); //CoverSet List

                if (rnk == 0)
                {
                    Can981 = CsubB;
                }       //(excludable candidates)
                else    //if(rnk>0){

                //  rank=k
                //    Consider the case of covering n-BaseSet with (n+k)-CoverSet.
                //    In order to be an analysis algorithm, the following conditions must be satisfied.
                //        1:(n+k)-CoverSet completely covers n-BaseSet.
                //        2:(k+1) of the (n+k) links of CoverSet have elements in common which are not included in the n-BaseSet.
                //    When these conditions are satisfied, the elements of the intersection of condition 2 are not true.
                {
                    bool SolFound = false;
                    Can981.Clear();
                    foreach (int n in CsubB.noBit.IEGet_BtoNo())
                    {
                        foreach (int rc in CsubB._BQ[n].IEGetRC())
                        {
                            int kc = CoverSetLst.Count(Q => Q.rcnBit.IsHit(n, rc));
                            if (kc == rnk + 1)
                            {
                                Can981.BPSet(n, rc);
                                SolFound = true;
                            }
                        }
                    }

                    if (!SolFound)
                    {
                        continue;
                    }
                }
                ++GeneralLogicGen2.ChkCov2;                       //*****

                BasCov.addCoverSet(CoverSetLst, HC981, Can981, rnk);
                if (_chkX2)
                {
                    string st = $"{_jkc_++}      ◆CoverSet:";
                    foreach (var P in CoverSetLst)
                    {
                        st += $" {P.ToAppearance()}";                                     //#### debug print
                    }
                    WriteLine(st);
                }
                yield return(BasCov);

LNextSet:
                continue;
            }
            yield break;
            #endregion CoverSet generator
        }