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36 defined recursively.) |
36 defined recursively.) |
37 |
37 |
38 \item Assume the concatenation operation of two strings is |
38 \item Assume the concatenation operation of two strings is |
39 written as $s_1 @ s_2$. Define the operation of |
39 written as $s_1 @ s_2$. Define the operation of |
40 \emph{concatenating} two sets of strings. This operation |
40 \emph{concatenating} two sets of strings. This operation |
41 is also written as $\_ \,@\, \_$. |
41 is also written as $\_ \,@\, \_$. According to |
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42 this definition, what is $A \,@\, \{\}$ equal to? |
42 |
43 |
43 \item Assume a set $A$ contains 4 strings and a set $B$ |
44 \item Assume a set $A$ contains 4 strings and a set $B$ |
44 contains 7 strings. None of the strings is the empty |
45 contains 7 strings. None of the strings is the empty |
45 string. How many strings are in $A \,@\, B$? |
46 string. How many strings are in $A \,@\, B$? |
46 |
47 |