diagonal: Palma de Mallorca invitation tournaments, was one of the leading series around fifty years ago:
Eight editions, annually from 1965 to 1972 (including the FIDE Interzonal from 1970). Twice winners, sole or shared, at Palma de Mallorca are <Bent Larsen>, <Viktor Korchnoi>, and surprising <Oscar Panno>.
All post-war world chess champions (then) did participate at Palma de Mallorca series: <Botvinnik, Smyslov, Tal (winner 1966), Petrosian, Spassky, and Fischer (winner of IZT 1970)>, meaning no less than four world chess champions did play but not win at Palma de Mallorca!
Mikhail Tal triumphed as clear first in 1966, ahead of Pomar and Portisch who shared second place, followed then by Ivkov.
In 1967, Bent Larsen surpassed the two former soviet world champions, Botvinnik and Smyslov, who finished as joint runners-up, followed by some of the usual suspects, Portisch, Gligoric, Ivkov: Palma de Mallorca (1967)
The edition of 1968 saw Petrosian the reigning world champion, Spassky his challenger, Korchnoi, the runner-up of the candidate's final and Larsen the previous winner. Viktor Korchnoi who also took Wijk aan Zee in January the same year, won outright and unbeaten ahead of Larsen and Spassky, Petrosian, Gligoric, Ivkov: Palma de Mallorca (1968)
Bent Larsen won again outright at Palma de Mallorca in 1969, surpassing Petrosian, Korchnoi, Hort, and Spassky, the new crowned world champion: Palma de Mallorca (1969)
The Interzonal in 1970 with 24 players in a round robin, was dominated by Bobby Fischer, he won overwhelmingly at 3.5 points ahead of joint 2.-4. Larsen, Geller, and IM Hübner (Spassky defending world champion, Petrosian, and Korchnoi already qualified for the candidate's matches, thus all absent): Palma de Mallorca Interzonal (1970)
Oscar Panno co-won in 1971, together with Ljubomir Ljubojevic, ahead of joint Portisch and Reshevsky, Larsen sharing sixth place, and won again a year later, as best on tie-break in 1972, surpassing three prominent soviet players, co-winner Korchnoi, top-seeded Polugaevsky, and Averbakh.
The French Wikipedia provides a good overview, summary of the Palma de Mallorca series: https://fr.wikipedia.org/wiki/Tourn...