Give context-free grammars that generate the following languages.

Question

1. L1={a^n b^2n c^m |n,m>0}

2. L2 = {a^3n b^2n | n ≥ 0}, the alphabet is ∑={a,b}

3. L3 = {a^i b^j c^k | i, j, k ≥ 0 and i+j <= k}, the alphabet is ∑={a,b,c}