Given Language is L$= \left \{ a^{i}b^{j}c^{k}d^{l} | i=k\ or\ j=l \right \}$
For Simplicity we can consider it as
L=$= \left \{ a^{k}b^{j}c^{k}d^{l} \right \}\cup \left \{ a^{i}b^{l}c^{k}d^{l} \right \}$
So the given language is Either n number of a's followed by n number of c's or n number of b's followed by n number of d's.
The machine which will accept the above language will be nondeterministic pushdown automata (NPDA).
Hence the given language is Context free language (CFL).
And another language is L=$\left \{ a^{m}b^{n}c^{m}d^{n} \right \}$ which is not context free language.
It can,t be accepted by NPDA.First you have push all a's then push all b's .Now a's has to match with c's but top of stack is b's.
Machine will stuck at that time since there is no way to match a's with c's and b's with d's.
So it can,t be accepted by NPDA .Given Language is Context Sensitive(CSL).
