Function numVal

src/compute-engine/rubi/rubi-utils.ts:1403–1410

(f: Expression)

 * (Rubi SumBaseQ companions); null when not a sum base */
function sumBaseTerms(u: Expression): Expression[] | null {
  if (u.operator === 'Add' || u.operator === 'Subtract') return sumTermsX(u);
  if (u.operator === 'Power' && u.ops) {
    const k = realNum(u.ops[1]);
    if (k !== null && Number.isInteger(k) && Math.abs(k % 2) === 1)
      return sumBaseTerms(u.ops[0]);
  }
  return null;
}
const sumBaseQ = (u: Expression): boolean => sumBaseTerms(u) !== null;
const negSumBaseQ = (u: Expression): boolean => {
  const ts = sumBaseTerms(u);