# free context – How the language \$ {a ^ nb ^ mc ^ nd ^ m | n geq1, m geq1 } \$ is used to verify if the formal and real parameters are the same?

How the language works $$L = {a ^ nb ^ mc ^ nd ^ m mid n geq1, m geq1 }$$ Summarize the problem of verifying that the number of formal parameters in the declaration of a procedure matches the number of actual parameters in a use of the procedure?

I just did not understand what each of the variables $$a, b, c, d, n$$ Y $$m$$ will it represent? It seems $$1 ^ {st}$$ pair $$(n, m)$$ It is for formal parameters and then for real ones. But I did not understand why there is $$a$$ Y $$b$$? Could not a single variable be enough?