#let q4 = [
4. (Fun with regex) Give regular expressions describing the following languages. In all cases, the alphabet is ${0, 1}$.

  + ${w | w "contains with at least three 1s"}$.

    $Sigma^ast (1 Sigma^ast)^3$

  + ${w | w "contains exactly two 0s and at least two 1s"}$.

    = TODO

  + ${w | "every odd position in" w "is 1"}$.

    $(10 union 11)^ast (1 union epsilon.alt)$
]
