#MAple command for solving the recurrence a(n)-a(n-1)-a(n-2)=0, with initial conditions a(0)=0, a(1)=1
rsolve({a(n)-a(n-1)-a(n-2)=0, a(0)=0,a(1)=1},a(n));

#ALSO OK

rsolve({a(n)-a(n-1)-a(n-2)=0, a(0)=0,a(1)=1},{a(n)} );

#THE REASON I MESSED UP IN CLASS WAS THAT a was already committed before