Construct contextfree grammars that generate the following l
     Construct context-free grammars that generate the following languages. In all cases, sigma = {0, 1}.  middot  {0^2n1^n: n greaterthanorequalto 0}  {w: w contains at least three 1s}  {w: the length of w is odd and its middle symbol is 0} 
  
  Solution
Answer:
1. S->A|epsilon
A->00AB|001
B->1
2.
X Y1Y1Y1Y
Y 0Y | 1Y | epsilon
3.
S 0S0 | 0S1 | 1S0 | 1S1 | 0

