Problem 1 (20 points): Show that for any two regular expressions r and s the following is true:
$$(r^*s^*)^* = (r \cup s)^*$$
For example, taking r = 10*11(01) and s = (1∪ɛ)11*(01), the above equality implies that
$$( ( 10*11(0 \cup 1))^* ( (1\cupɛ)11*(0 \cup 1) )* )^* = ( ( 10*11(0 \cup 1) ) \cup ( (1\cupɛ)11*(0 \cup 1)))^*$$
r
S
r
S
Note that proof by example and proof by vague-o-logy (i.e., vague descriptions) are
not valid proof methods.
Hint: Show that (r* s*)* ⊆ (r + s)* and (r* s*)* ⊇ (r + s)*. In other words, show that:
• If a string is in (r*s*)* then the string is also in (r + s)*.
• If a string is in (r + s)* then the string is also in (r* s*)*.