true, if equal(f1, f2) is known to be equivalent to f1 == f2
equal(f1, f2)
f1 == f2
Order.fromScalaOrdering(toScalaOrdering).order(x, y) = this.order(x, y)
Order.fromScalaOrdering(toScalaOrdering).order(x, y)
this.order(x, y)