By next Thursday's class, draw concise AST's for the following tiger
expressions and label each with the "result register" attribute for
Sethi-Ullman register allocation. Pick any one of the attributed AST's
and label EACH node with the associated HERA instructions (feel free
to find some creative way to use labels so you don't have to re-write
many copies of the same line).

Don't spend more than 20 minutes on this.

The examples expressions are:

    1 + 2 + 3 + 4
    5 * 6 + 7 * 8
    (1 + 2 ; 5)    /* a sequence expression */