private void remove(int c){
		L[R[c]] = L[c];
		R[L[c]] = R[c];
		for(int i = D[c]; i != c; i = D[i]){
			for(int j = R[i]; j != i; j = R[j]){
				U[D[j]] = U[j];
				D[U[j]] = D[j];
				-- S[C[j]];
			}
		}
	}