  We argue by example that conditionally clean ancillae, recently described by
[NZS24], should become a standard tool in the quantum circuit design kit. We
use conditionally clean ancillae to reduce the gate counts and depths of
several circuit constructions. In particular, we present:
  (a) n-controlled NOT using 2n Toffolis and O(log n) depth given 2 clean
ancillae.
  (b) n-qubit incrementer using 3n Toffolis given log*(n) clean ancillae.
  (c) n-qubit quantum-classical comparator using 3n Toffolis given log*(n)
clean ancillae.
  (d) unary iteration over [0, N) using 2.5N Toffolis given 2 clean ancillae.
  (e) unary iteration via skew tree over [0, N) using 1.25 N Toffolis given n
dirty ancillae.
  We also describe a technique for laddered toggle detection to replace clean
ancillae with dirty ancillae in all our constructions with a 2x Toffoli
overhead. Our constructions achieve the lowest gate counts to date with
sublinear ancilla requirements and should be useful building blocks to optimize
circuits in the low-qubit regime of Early Fault Tolerance.
