Thanks a lot Alejandro. I did not use a menu for creation of the input lines. I simply typed "*" for multiplication, as I prefer to have a multiplication sign rather than a space between the two multiplied arguments.

Thanks a lot Alejandro. I did not use a menu for creation of the input lines. I simply typed "*" for multiplication, as I prefer to have a multiplication sign rather than a space between the two multiplied arguments.

The term "thetaScaleDefinition" includes the "old to new" rule.

I am trying to implement a "multiple time scale" solution to a problem, whereby these kind of expressions are required to be developed. The complete model is too complex to include here, and actually not connected to this problem.

I've tried the same expression without using subscripts (i.e using D1,D2 instead of D₁,D₂ ) but the problem persists.

The term "thetaScaleDefinition" includes the "old to new" rule.

I am trying to implement a "multiple time scale" solution to a problem, whereby these kind of expressions are required to be developed. The complete model is too complex to include here, and actually not connected to this problem.

I've tried the same expression without using subscripts (i.e using D1,D2 instead of D₁,D₂ ) but the problem persists.