Which is bigger

The solution

type GreaterThan<A extends number, B extends number, C extends unknown[] = []> =
  C['length'] extends A
    ? false
    : C['length'] extends B
      ? true
      : GreaterThan<A, B, [...C, unknown]>

The common wrong answer

type GreaterThan<A extends number, B extends number, C extends unknown[] = []> =
  C['length'] extends B
    ? true
    : C['length'] extends A
      ? false
      : GreaterThan<A, B, [...C, unknown]>

Both tests are right; the order is not. When `A` and `B` are equal the counter reaches them on the same step, and whichever question is asked first wins. Asking about `B` first answers `true` for `GreaterThan<2, 2>` — equal is reported as greater, and only the equality case ever reveals it.

Line by line

1. C['length'] extends A ? false

   Reaching `A` first means `B` is at least as large, so `A` cannot be strictly greater. Putting this branch first is what makes the comparison strict rather than "greater or equal".

2. [...C, unknown]

   One tick of the counter. The tuple is never read — only its length is — so it is the cheapest possible way to hold a number that can go up by one.

3. GreaterThan<0, 5>

   The counter starts at zero, so this is decided before a single step is taken: `A` is reached immediately and the answer is `false`.

Takeaway

When two conditions can fire on the same step, their order is the specification. Comparison types are almost always correct on the unequal cases and wrong on the tie.