1. L ={ a^n b^m c^x d^y | n=m or x=y} CFL but not DCFL
PDA have to copies ::
COPY 1: push a's , pop b's ---> in end stack empty , c ->ignore , d->ignore
COPY 2: a->ignore , b->ignore,push c's , pop d's ---> in end stack empty
2. L ={ a^n b^x c^m d^y | n=m or x=y} CFL but not DCFL
PDA have to copies ::
COPY 1: push a's , b ->ignore ,pop c's ---> in end stack empty , d->ignore
COPY 2: a->ignore , push b's, c->ignore,pop d's ---> in end stack empty,