@Markiyan Hirnyk It is a table not an array. I think that makes the difference.

@Markiyan Hirnyk It is a table not an array. I think that makes the difference.

I had to change the round brackets in T(a,b) to square brackets, but then your answer worked. Thanks.

I had to change the round brackets in T(a,b) to square brackets, but then your answer worked. Thanks.