DataType[exp, type] = True defines the object exp to have data-type type. DataType[exp1, exp2, ..., type] defines the objects exp1, exp2, ...to have data-type type. The default setting is DataType[__, _] := False. To assign a certain data-type, do, e.g., DataType[x, PositiveInteger] = True.
See also: DeclareNonCommutative.
NonCommutative is just a data-type.
Since "f "and "g" have DataType NonCommutative the function DotSimplify extracts only "a" out of the noncommutative product.
Certain FeynCalc objects have DataType PositiveInteger set to True.
PowerSimplify uses the DataType information.
The FeynCalc Book | D0 | DeclareNonCommutative |