fibonacci(n) := fibonacciHelper([[1,0],[0,1]], n);

fibonacciHelper(M(2), n) :=
	let
		N := [[1,1],[1,0]];
	in
		M[1,1] when n <= 1
	else
		fibonacciHelper(matmul(M, N), n - 1);

matmul(A(2), B(2)) [i,j] := sum( A[i,all] * B[all,j] );