Rakudo does not yet attempt parallelization of any Junctions. Even if/when it one day does, overhead will sometimes dominate, especially when trying to parallelize really tiny computations. I'm curious what you meant by "duplicate removal phase" and would enjoy reading an elaboration of that.

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Here are the two rules which drive how the grammar distinguishes a Whatever * from a multiplication *:

1. If a token appears where an operator is allowed and there's a corresponding operator definition then it's that operator.

   For example, an operator is allowed between values, and an infix:<+> definition is in scope in ordinary code (here's the built in Numeric role's contribution to that definition), so the token + in 2 + 3 is treated as invoking infix:<+>. The same thing applies for other infix operators including multiplication with Infix:<*>.

2. If an asterisk is NOT treated as an operator and appears where a value is allowed then it's a Whatever.

   For example, 2 + 3 includes the two values 2 and 3 and there is no prefix:<*> so one could write * + * to express "Whatever plus Whatever".