wordAB? abWordABWordWord.
abab ababababab
AB A B AB j A a_1, a_2, \dots, a_n B j .
ABOAB OAB .
ABAB112AB ...
ab 1AB 2.
ABABAB.
ab ab 1abab 2abab.
"ABC"
wordAB? abWordABWordWord.
abab ababababab
AB A B AB j A a_1, a_2, \dots, a_n B j .
ABOAB OAB .
ABAB112AB ...
ab 1AB 2.
ABABAB.
ab ab 1abab 2abab.
"ABC"