b 7 + ▁( follow ed ▁by ▁K xa 5 ▁Ra 1 # ), ▁while ▁the ▁black ▁ro ok ▁on ▁c 8 ▁def ends ▁against ▁R xc 5 # . ▁ ▁T arr as ch ▁played ▁the ▁ingen ious ▁inter ference ▁move ▁ 3 1 . B c 7 ! ▁( known ▁as ▁a ▁Pla ch ut ta ▁inter ference ▁because ▁the ▁pieces ▁both ▁move ▁orth og on ally ). ▁ ▁This ▁blocks ▁off ▁both ▁def ences , ▁and ▁whatever ▁piece ▁capt ures ▁becomes ▁over loaded . ▁ ▁That ▁is , ▁if ▁ 3 1 ... R xc 7 , ▁the ▁ro ok ▁is ▁over loaded , ▁having ▁to ▁look ▁after ▁both ▁the ▁key ▁squares , ▁since ▁the ▁queen ▁is ▁blocked ▁from ▁b 7 . ▁ ▁So ▁White ▁would ▁play ▁ 3 2 . Q b 7 + ▁R x b 7 , ▁def lect ing ▁the ▁ro ok ▁from ▁defence ▁of ▁c 5 , ▁allowing ▁ 3 3 . R xc 5 # . ▁But ▁if ▁Black ▁plays ▁instead ▁ 3 1 ... Q xc 7 , ▁the ▁queen ▁blocks ▁off ▁the ▁ro ok ' s ▁defence ▁of ▁c 5 ▁and ▁becomes ▁over loaded : ▁ 3 2 . R xc 5 + ▁Q xc 5 ▁def lect s ▁the ▁queen ▁from ▁defence ▁of ▁b 7 , ▁allowing ▁ 3 3 . Q b 7 + ▁K xa 5 ▁ 3 4 . R a 1 # . ▁ ▁Black ▁actually ▁res igned ▁after ▁this ▁move . ▁ ▁In ▁the ▁game ▁against