Problem

The Auction:

South opened tamely with 1♦. West overcalled 2♥ (weak preempt, 6 hearts). North responded 2♠ (5+ spades). East rose to 3♥ (3-card support to hearts). South jumped to 4♠ with his meager doubleton, pushed by his 6-4-2-1 distribution and 16 HCP.

West passed. North got the infection and cuebid 5♦ to show first round control in diamonds. East passed. South raised to 6♦.  West and North passed. East bid 6♥. Now South and West passed.

North declared 7♦. West led the ♠ J. How can South win 13 tricks?

Vul: both

Contract: 7♦ by South.