4 ▁N d 7 ) ▁was ▁introduced ▁by ▁K eres ▁at ▁the ▁ 1 9 6 2 ▁C andid ates ' ▁tournament , ▁and ▁was ▁popular ▁for ▁several ▁years . ▁He ▁also ▁popular ized ▁the ▁K eres ▁Def ence ▁( 1 . d 4 ▁e 6 ▁ 2 . c 4 ▁B b 4 +) ▁and ▁a ▁system ▁on ▁the ▁Black ▁side ▁of ▁the ▁English ▁Open ing ▁that ▁runs ▁ 1 . c 4 ▁e 5 ▁ 2 . N c 3 ▁N f 6 ▁ 3 . g 3 ▁c 6 . ▁ ▁K eres ▁published ▁ 1 8 0 ▁problems ▁and ▁ 3 0 ▁studies , ▁including ▁a ▁ro ok ▁ending ▁that ▁won ▁a ▁first ▁prize ▁in ▁ 1 9 4 7 ." ▁ ▁K eres ▁won ▁top - class ▁tournament s ▁from ▁the ▁mid - 1 9 3 0 s ▁into ▁the ▁mid - 1 9 7 0 s , ▁a ▁span ▁of ▁ 4 0 ▁years , ▁and ▁won ▁major ▁events ▁in ▁western ▁Europe , ▁eastern ▁Europe , ▁the ▁Soviet ▁Union , ▁South ▁America , ▁and ▁North ▁America . ▁Bot v inn ik , ▁by ▁contrast , ▁never ▁competed ▁in ▁the ▁Amer icas ▁during ▁his ▁career . ▁ ▁His ▁rival ▁Samuel ▁Res he v sky ▁said ▁that ▁K eres ▁failed ▁to ▁become ▁world ▁champion ▁because ▁he ▁lack ed ▁a ▁k iller ▁instinct ▁and ▁" was ▁too ▁m ild ▁a ▁person ▁to ▁give ▁his ▁all ▁in ▁order ▁to ▁defeat ▁his ▁oppon ents . ▁He ▁took ▁everything , ▁including ▁his ▁ch