Function sumBaseTerms

src/compute-engine/rubi/rubi-utils.ts:1334–1342

sum terms of a base (Add/Subtract), through odd literal powers * (Rubi SumBaseQ companions); null when not a sum base

(u: Expression)

 * elliptic branch-phase cluster: e^{iπ/4} errors came from taking the root
 * of the whole quotient instead of the split). */
function rtExpr(u: Expression, n: number | Expression): Expression {
  const ce = u.engine;
  const nn = typeof n === 'number' ? ce.number(n) : n;
  const nv = realNum(nn);
  const v = safeSimplify(u); // ≈ TogetherSimplify
  if (nv === null || !Number.isInteger(nv) || nv < 1)
    return v.pow(ce.One.div(nn)).evaluate();
  return rtAux(v, nv);
}

/** literal principal root u^(1/n) (Rubi NthRoot) */
function nthRoot(u: Expression, n: number): Expression {