append method
Implementation
@override Tuple3<T1, T2, T3> append(Tuple3<T1, T2, T3> t1, Tuple3<T1, T2, T3> t2) =>
new Tuple3<T1, T2, T3>(_value1Monoid.append(t1.value1, t2.value1), _value2Monoid.append(t1.value2, t2.value2), _value3Monoid.append(t1.value3, t2.value3));