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Let $\sum = \{0,1\}$ and let $D = \{w|w$  $\text{contains an equal number of occurrences of the sub strings 01 and 10}\}.$
Thus $101\in D$ because $101$ contains a single $01$ and a single $10,$ but $1010\notin D$ because $1010$ contains two $10's$ and one $01.$ Show that $D$ is a regular language.

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