Find gra

mm

ars for $=\{$a

$,$ b$\}$ th

a

t genera

te the sets of

$($

$)$

a

all strings with ex

a

ctly two

a

$$s$.$

$($b$)$

all strings with

a

t le

ast two

a

$$s$.$

$($c$)$

all strings with no more th

a

n three

a

$$s$.$

$($d$)$

all strings with

a

t le

ast three

a

$$s$.$

$($e$)$

all strings th

a

t st

art with

a a

nd end with b

$.$

$($f$)$

all strings with

n even numb

a

er of b$$s$.$