Question

Suppose Σ = {a,b,c,d} ,and regular expression

are:

1. [a b] ? [c d]

2.~dad?

show in standard notation and Write set of all the strings for above expressions?

Answer 1

1.

Regular Expression: (a+b+epsilon)(c+d)

Language in set: {c, d, ac, ad, bc, bd}

Explanation;

[ab]? means 0/1 letters from set of ab

[cd] one letter from set cd

2.

Regular expression: NONE

Language: {}

Because ~d should match literally but ~ is not in Σ

Otherwise if you think ~ is allowe

Regular Expression: ~da(epsilon+d)

Language in set: {~da, ~dad}

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