If we see..
L1: a^mb^nc^n|n,m>=1 CFL
L2:a^mb^mc^n|n,m>=1 CFL
L: L1 intersection L2 = a^nb^nc^n |n>=1 =CSL
That is not clouser under intersection
Bcoz PDA NOT POSSIBLE - WE NEED 2 COMPRESSION AT A TIME.
i'e 2 stack required.....but in PDA ONLY NEED 1 STACK
There for ANS is CSL ;