Function functionOfTrig

src/compute-engine/rubi/rubi-utils.ts:3166–3173

FunctionOfTrig[u, x]: the common linear trig argument, or the False symbol.

(
  ce: ComputeEngine,
  u: Expression,
  x: string
)

/** `a + b·trig[linear arg]` (x-free constant part `a`, single trig term) →
 * `{head, a, b, arg}`, else null. */
function trigBinomParts(
  ce: ComputeEngine,
  e: Expression,
  x: string
): TrigBinom | null {
  if (e.operator !== 'Add' || !e.ops) return null;
  let a: Expression = ce.Zero;
  let mono: TrigMono | null = null;
  for (const t of e.ops) {
    if (!t.has(x)) {