Function combine

src/compute-engine/library/combinatorics.ts:321–332

(
          start: number,
          combo: Expression[]
        )

          let steps = 0;
          for (let i = 2n; i <= m; i++) {
            if ((++steps & 0xffff) === 0) checkDeadline(ce._deadlineFrame);
            const next = a + b;
            a = b;
            b = next;
          }
          result = b;
        }

        // Reflection formula: F(−m) = (−1)^{m+1} F(m). The previous code built
        // a malformed `Negate(Fibonacci, m)` (two operands) → an Error.
        if (k < 0n && m % 2n === 0n) result = -result;
        return ce.number(result);
      },
    },