“ The right to counsel at sentencing is no different. As in these other cases, the right being asserted relates to 'the very integrity of the fact-finding process.' Linkletter v. Walker, 381 U.S. 618, 639, 85 S.Ct. 1731, 1743, 14 L.Ed.2d 601 (1965) ; cf. Roberts v. Russell, 392 U.S. 293, 88 S.Ct. 1921, 20 L.Ed.2d 1100 (1968) . As we said in Mempa, 'the necessity for the aid of counsel in marshaling the facts, introducing evidence of mitigating circumstances and in general aiding and assisting the defendant to present his case as to sentence is apparent.' 389 U.S. at 135, 88 S.Ct. ”

“ Wainwright, 372 U.S. 335, 83 S.Ct. 792, 9 L.Ed.2d 799 (1963) ; at certain arraignments, Hamilton v. State of Alabama, 368 U.S. 52, 82 S.Ct. 157, 7 L.Ed.2d 114 (1961) ; and on appeal, Douglas v. People of State of California, 372 U.S. 353, 83 S.Ct. 814, 9 L.Ed.2d 811 (1963) , have been applied retroactively. ”