How to affect values and percentages contribution based on specific dimension?

Hello, we wish to have a calc rule with two expressions, the first calculates Percentage depending on Values, the second calculates Values depending on Percentages.

The meaning of the Percentage is "product mix", that is the contribution of an item on a category. I mean that at category level the percentage must be 100% . So we need to fix "category" level in the rule.

The rule should be  Value = Perc * Value.level([prod].[cat])  As this is not possible because Value is both RHS and LHS we used:

rule1:

expr1: Perc = Value / Value.level([prod].[cat])

expr2: Value = Perc * TmpValue.level([prod].[cat])