def Topology_Uniques_Apply(self,topology):
        res=True
        n=0
        while (res and n<25):
            n+=1
            res=self.Topology_Unique_Apply(topology)

        topology=self.Topology_Initial()

        return res

            
    ##!
    ##! Locate 'uniques'.
    ##!
    
    def Topology_Unique(self,topology):
        uniques=[]
        
        for r in range(self.M):
            for s in range(self.M):
                if (self.S[r][s]==0):
                    if (len(topology[r][s])==1):
                        uniques.append([r,s,topology[r][s]])

        return uniques
    
    ##!
    ##! Apply
    ##!
    
    def Topology_Unique_Apply(self,topology):
        uniques=self.Topology_Unique(topology)
        for unique in uniques:
            r=unique[0]
            s=unique[1]
            value=unique[2].pop()

            self.S[r][s]=value
            
        return uniques

    
    ##!
    ##! Remove (zero) cell, for puzzle generation.
    ##!