Use all the digits 1 to 9 create three 3-digit numbers, which, when multiplied together creates the highest value possible.

(In reply to

re(2): How to do! by Juggler)

I am not quite sure what you mean. It sounds to me that you are putting forth an argument of the form:

Given condition A, quantity Q takes a maximum when condition B holds.

Thus, for any condition A' that is similar (semantically?) to A, we have that, given condition A', quantity Q again takes a maximum when condition B holds.

(here, we have specifically

A="sum of numbers is fixed"

A'="sum of digits is fixed"

Q="product of numbers"

B="numbers are all equal"

)

If that is your argument, it certainly falls short of a verification. It is at best solid intuition.