Function is_counter_type 

pub fn is_counter_type(type_name: &str) -> bool

Whether a declared type name is a COUNTER CRDT — one whose readable value is an Int total.

The counters are the CRDTs an Int literal can initialize: Let n: Tally be 5. is a counter at five, and the reference tier already projects a counter to its Int total on the wire. A set or a sequence has no such reading, so an Int beside one stays an error.