[less than 10 +]
a:        1 .. 9
b:        1 .. 9-a
op:       +
score:    2
size:     10

[less than 10 -]
a:     2 .. 9
b:     1 .. a-1
op:    -
score: 3
size:  5


[less than 100 *]
a:     1 .. 10
b:     1 .. 10
op:    *
score: 5 
size:  5