While he was in Ankara in 1967-68 he wrote to Serre with ideas which would eventually be formulated as the Deligne -Langlands conjecture; this was proved eventually by Kazhdan and Lusztig.
Habang siya ay sa Ankara sa 1967-68 wrote siya sa Serre sa ideya na kung saan ay sa wakas ay formulated na ang Deligne-Langlands haka-haka; ito ay proved huli sa pamamagitan ng Kazhdan at Lusztig.