x
abc
abc+x
a+b+c
a*b+c-d/e
10
-20
10+a-20--x
(a-1)
-20*(3+4-(x*y))
3*(4+5)
((x+y)*z)/2+((x))-(q/3)*500
Ill-formed expressions below
.x.
(x+3)*
x++3
(a-b(x))
)(x+y)*z)/2+((x))-(q/3)*500