A-F (A`-F`) - ; (: , !)
B A-E (A`-E`) - ;
C A-F (A`-F`) - , ;
D A-F (A`-F`) - , .
( 51), ( 52, ):
1 (2) A (A`), , A (A`) ----- ( ) B (B`), B (B`) _____ C (C`), C (C`) ----- D (D`), D (D`) _____ E (E`), E (E`) ----- F (F`), F (F`) (2-3 , , ) 1 (2) ----- A (A`) , , .