Have to condition a different customer name and concat

There are 2 things needed here.

1. We have customer table which can have a blank. If this is the case, we want to take the first and last name from a different columns.

I am trying to have a formula in this walkthru:

If {ADRES1.ADENTN} > ' '

then   {ADRES1.ADENTN} = {ADRES1.ADENTN}

else

({ADRES1.ADFNM} + {ADRES1.ADLNM})

2, As you see I would need to have a space between the First and Last names.