The LEFT function from Excel does not exist in TM1. We need to use SUBST instead.
Where you have a formula in Excel in A2 that is = LEFT ( A1, 4), where the contents of A1 is the string “ExploringTM1”, the formula will return the first 4 characters, i.e. “Expl”.
To achieve the same result in a TM1 Turbo Integrator process we need to use the SUBST function. A full discussion on SUBST can be found here, however briefly, the formula to replicate the Excel function illustrated above would be SUBST ( ‘ExploringTM1’, 1, 4);, in other words take the string (or the variable referred to that contains the string) and starting at position 1, take the next 4 characters (including that first character).
This applies to both Rules and Turbo Integrator processes.