text: since all four a , b , c , d should be distinct
code: if ( i == j ) : NEW_LINE INDENT continue NEW_LINE DEDENT for k in range ( j + 1 , n ) : NEW_LINE INDENT if ( i == k ) : NEW_LINE INDENT continue NEW_LINE DEDENT for l in range ( k + 1 , n ) : NEW_LINE INDENT if ( i == l ) : NEW_LINE INDENT continue NEW_LINE DEDENT DEDENT DEDENT