(a) For n ‰¥ 4, consider the strings made up of n bits - that is, a total of n 0's and l's. In particular, consider those strings where there are (exactly) two occurrences of 01. For example, if n = 6 we want to include strings such as 010010 and 100101, but not 101111 or 010101. How many such strings are there?
(b) For n ‰¥ 6, how many strings of n 0's and l's contain (exactly) three occurrences of 01?
(c) Provide a combinatorial proof for the following: For n ‰¥ 1,

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け1), nodd on 1 n n even.