if the following are true:

• Expression Stack at time t = [ [ ], [ [ function call with name: "__mul__" and arguments: args, ys ], rest ] ]
• Value Stack at time t = [ [ a, [ b, [ ] ] ], [ next_level, other_levels ] ]

then Value Stack at time (t + 1) = [ [ b ⋅ a, next_level ], other_levels ]