Solving: 1+2
is easy.
Proving that: 1+2=3
is not so easy. The problem is not understanding what the symbols 1,2 and 3 are, but understanding what the '+' does to the '1' and '2'.
But, once that is understood, 1+2 can be anything you want it to be, as long as the definition of '+' is understood.
1ove