If 1,1 occurs in last two places

#1

couldn’t understand the recurrence relation

if 1,1 occurs at the last places then what operation is being done here?

#2

@atkr030
Suppose you need to construct a binary string of length n and you have already constructed a string of length i, where i < n. If the element at the ith position is 1, then the element the (i + 1)th position cannot be a one.

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