A special characteristic decomposition of a regular semigroup S by disjoint subsemigroups is given. The subsemigroups involved in the decomposition and the interrelations among them are studied.
                    
                 
                
                    
                
            
        
            
            
            
            
            
                
            
                
            
                
            
                
            
                
            
                
                    
                
            
                
            
                
             
            
            
                
            
            
            
                
                    
                
            
            
            
            
                
            
            
             
            
                
            
            
            
                
                
                
                    
                       
The concepts of T-relation, of absolute and relative -complement ( being a T-relation) are introduced for a finite group G. A necessary and sufficient condition for the conjugacy of the relative -complements of a subgroup of G is given. This result generalizes a theorem of Gaschütz.
                    
                 
                
                    
                
            
        
        
        
            
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