//**********************************
//***      skeleton
// Written by Jarek Rossignac,  June 2006 
//**********************************
void computeSkeleton() {
  int tc=0;
  int r=1;
  for(int i=0; i<nt; i++) {Mt[i]=0;};  
  for(int i=0; i<nv; i++) {Mv[i]=0; if (valence[i]!=6) {Mv[i]=1;};};
  for(int i=0; i<nc; i++) {if ((Mt[t(i)]==0)&&(Mv[v(i)]==r)) {Mt[t(i)]=1; tc++;};};
  for(int i=0; i<nc; i++) {
     if (Mt[t(i)]==0) {
         int nbrs=0; 
         if((o(i)!=-1)&&(Mt[t(o(i))]==1)) {nbrs++;};
         if((r(i)!=-1)&&(Mt[t(r(i))]==1)) {nbrs++;};
         if((l(i)!=-1)&&(Mt[t(l(i))]==1)) {nbrs++;};
         if (nbrs>2) {Mt[t(i)]=1;};
         };
     };
    for(int i=0; i<nv; i++) {Mv[i]=0;};

/*  while (tc<nt) {
      for(int i=0; i<nc; i++) {if ((Mv[v(i)]==0)&&(Mt[t(i)]==r)) {Mv[v(i)]=r;};};
     for(int i=0; i<nc; i++) {if ((Mt[t(i)]==0)&&(Mv[v(i)]==r)) {Mt[t(i)]=r+1; tc++;};};
     r++;
     };
     /**/
  rings=r;
  }