I have that language S={w= a^n b^m c^m, n,m >=0}
How can i prove with the pumping lemma that it isnt regular? Can i use the concatenation closure and say its the language L1 = {w=a^n, n>=0} and L2 ={w= b^m c^m, m >=0} prove that L2 isnt regular so L1 L2 = S is not regular too?