0 QTRS
app(app(app(consif, true), x), ys) → app(app(cons, x), ys) app(app(app(consif, false), x), ys) → ys app(app(filter, f), nil) → nil app(app(filter, f), app(app(cons, x), xs)) → app(app(app(consif, app(f, x)), x), app(app(filter, f), xs))