alpha = 3 # good
beta = 123.23 # good
1 = 3 # bad (letters only on left)
a 3 # bad (no = sign)
1 + 2 / 3.4
1.2 + 3.2 + 42.3 + 3 * 17
1 + * 7 # bad
(1 + 2)/(7 - 3)
((3*7+1)/(1-3.2)) + (17/3)
((1-3) # bad - parens don't match