Operators

Everything a rule can do comes from a small set of operators: compare two numbers, add or subtract, combine conditions, guard a rule, or test membership in a list. There is nothing else — which is why rules stay readable.

Comparison operators

Operator	Meaning	Example
=	Equal	current_value = 5
!=	Not equal	current_value != 0
<	Less than	current_sum < 100
<=	Less than or equal	current_sum <= 99
>	Greater than	prev_sum > 0
>=	Greater than or equal	current_value >= -9

Equality is a single =

Use a single = for equality checks, not ==. Comparisons also do not chain: 0 < current_value < 10 is not valid — write current_value > 0 AND current_value < 10.

Arithmetic

You can use + and - inside comparisons:

prev_sum + current_value >= 0

This is identical to current_sum >= 0. Addition and subtraction are the only supported arithmetic operators — multiplication and division are not available (and are rarely needed for this domain).

Arithmetic binds more tightly than comparisons, so a + b > c means (a + b) > c.

Parentheses work as expected: (a + b) > c and a + b > c are equivalent here.

Combining conditions: AND, OR, NOT

AND

Both sides must be true:

current_sum >= 0 AND current_sum <= 99

The running total must stay in the range 0–99.

OR

At least one side must be true:

current_value = 1 OR current_value = -1

Only 1 and -1 are allowed.

NOT

Inverts a condition:

NOT current_value IN (0, 5, 10)

Equivalent to current_value NOT IN (0, 5, 10) — see the membership section below for the cleaner form.

Precedence

NOT binds most tightly, then AND, then OR. This means:

a OR b AND c    →    a OR (b AND c)

Use parentheses whenever the intent might be ambiguous:

(prev_sum > 50 OR step_index = 0) AND current_value > 0

Conditional rules: IF…THEN

IF…THEN lets you write rules that only apply under certain conditions. When the IF guard is false, the rule is skipped — it neither passes nor fails. Skipped rules never block a move.

Only on the first step, the value must be positive:

IF step_index = 0 THEN current_value > 0

Steps 1, 2, 3, … are unaffected by this rule. Only step 0 is constrained.

When the sum is large, the player must reduce it:

IF prev_sum > 50 THEN current_value < 0

If prev_sum is 50 or less, the rule is skipped. If it exceeds 50, only negative values pass.

On the last step, the sum must hit the target:

IF isLastStep THEN current_sum = 100

Every intermediate step is free; only the final step is constrained to land on 100.

Membership tests: IN and NOT IN

Test whether a value is (or is not) in a specific set of numbers.

IN

current_value IN (1, 2, 3, 4, 5, 6, 7, 8, 9)

The candidate must be one of the listed values. The list is comma-separated and enclosed in parentheses.

NOT IN

current_value NOT IN (0, 5, 10, 15, 20)

The candidate must not be any of the listed values. NOT IN is two separate words — NOTIN is not recognized.

More examples

highest_digit(current_value) IN (1, 3, 5, 7, 9)   -- leading digit must be odd
prev_sum NOT IN (11, 22, 33, 44, 55)              -- sum must not be a double

See also

• Decimal places — the derived variables these operators are usually applied to, and how != and NOT IN behave when they are null.
• Quantifiers — EVERY and SOME, for conditions over individual digits.
• Common mistakes — uppercase keywords, ==, chained comparisons.
• Language reference — the formal grammar and precedence table.