code: private boolean hasOnlyPlainBonds(int v, IBond allowedDoubleBond) {
          int count = 0;
          for (int neighbor : graph[v]) {
              IBond adjBond = edgeToBond.get(v, neighbor);
              // non single bonds
              if (adjBond.getOrder().numeric() > 1) {
                  if (!allowedDoubleBond.equals(adjBond)) {
                      return false;
                  }
              }
              // single bonds
              else {
                  if (adjBond.getStereo() == UP_OR_DOWN || adjBond.getStereo() == UP_OR_DOWN_INVERTED) {
                      return false;
                  }
                  count++;
              }
          }
          return count > 0;
      }
docs: Check that an atom (v:index) is only adjacent to plain single bonds (may be a bold or
  hashed wedged - e.g. at fat end) with the single exception being the allowed double bond
  passed as an argument.
  
  @param v atom index
  @param allowedDoubleBond a double bond that is allowed
  @return the atom is adjacent to one or more plain single bonds