Which makes no sence, Why would you emulate something, when it has it built-in :\
Makes perfect sense.
The thing is, a GBA emulator, especially to those who previously owned a GBA, is not so far-fetched.
When flashcarts began arriving for the GBA, people were finding that the physical act of inserting a GBA cart disabled the GB/GBC built-in - and that they could not run GB/GBC ROM images from their GBA flashcart. Hence emulation was the answer (and Goomba did the job admirably) - although the GBA had a GB/GBC system built-in, flashcart owners had to resort to emulation.
Fast-forward to the present day, and people find that their slot-1 solutions do not cut the mustard for GBA usage, in a similar way to the old GB/GBC issue with GBA flashcarts. The DS does indeed, to the casual user, appear to be a
lot more powerful than the GBA - would emulation not be possible? Of course, we know that the DS is not actually that meaty in the CPU department, and hence emulation is extremely unlikely to be playable.
Of course, the OP neglected to search and thus shows his ignorance of how to behave as a newbie, but that aside - his reasons for asking his question are not so far-fetched. And having seen why a GB/GBC emulator made perfect sense for GBA owners, it does make some kind of sense for a GBA emulator on a DS.
D.