Function pickBy

src/compute-engine/rubi/rubi-utils.ts:1445–1451

(...preds: ((f: Expression) => boolean)[])

  if (rtAuxDepth > 40) {
    if (process.env.RUBI_DEBUG_RT)
      console.error(`rtAux depth cap: ${u.toString().slice(0, 120)}`);
    return nthRoot(u, n);
  }
  rtAuxDepth++;
  try {
    return rtAuxBody(u, n);
  } finally {
    rtAuxDepth--;
  }
}