下面这几道题是一个朋友的练习题，他目前对这个一点概念都没有，看书也
看的似是而非，求解答并不是为了拿分数，是为了能知道一点，然后有点信心
继续学下去。哪位高手能给个答案和简单的解释，不胜感激！！！
1 Σ = { 0, 1 }. Show in details beginning from the trivial languges, Ø, { 0 } and { 1 } how the following languages of RAT(S) is formed.
a) words that consist of even amount of nulls (00 0000..)
b) words which have partial word (suffix or prefix) 101
c) words not including two ones one after another, so theres no 11 in words.
2 Make the grammatical linear to the right, producing the lanquages mentioned in the exercise 1 (for each languages their own grammaticism). Produce with the help of your grammaticism the words 000000, 0100101110 and 010001. Also make a grammaticism linear to the left and show how you direct the word 010001 using this grammaticism.
3 Σ = { 0, 1 }. Is RAT(S) = 2S* true ? Why ?
4 L and K are languages and their context-free grammaticism are GL = (VL, S, PL, SL) and GK = (VK, S, PK, SK). Make context-free grammaticism for languages LÈK, L×K and L*. You may assume that VLÇVK = S.