+ Accumulator* prev_accumulator;
+ assert(pos.state()->previous);
+ if (pos.state()->previous->accumulator.computed_accumulation) {
+ prev_accumulator = &pos.state()->previous->accumulator;
+ }
+ else {
+ assert(pos.state()->previous->previous);
+ assert(pos.state()->previous->previous->accumulator.computed_accumulation);
+ prev_accumulator = &pos.state()->previous->previous->accumulator;
+ }
+