Grammar for ${a^n b^n c^{n+m}}$ Can we define a grammar for the following language?

$$L = \{a^n b^n c^{n+m} | n,m&gt;=0\}\,.
$$

I can define one for this:
$$L=\{a^nb^n|n,m&gt;=0\}
$$


  S --> aSb | λ  


or this one:
$$L=\{b^nc^{n+m}|n,m&gt;=0\}
$$  


  S --> Ac
  A --> bSc | Sc | λ


but I can't solve the first one, any hint?
GRAMMAR FOR THE LANGUAGE:{a^n b^n c^n/n>=1}

S->abc|A

A->aABc|abc

cB->Bc

bB->bb

FOR EXAMPLE:INPUT STRING aaabbbccc when n=3

S->A

->aABc

->aaABcBc (A->aABc)

->aaabcBcBc   (A->abc)

->aaabBccBc   (cB->Bc)

->aaabBcBcc   (cB->Bc)

->aaabbcBcc   (bB->bb)

->aaabbBccc   (cB->Bc)

->aaabbbccc   (bB->bb)