for a being Element of Benzene holds
( ( a = 0 implies a ` = 3 ) & ( a = 3 implies a ` = 0 ) & ( a = 1 implies a ` = 3 \ 1 ) & ( a = 3 \ 1 implies a ` = 1 ) & ( a = 2 implies a ` = 3 \ 2 ) & ( a = 3 \ 2 implies a ` = 2 ) )