one arg +

[elenam]

This may be connected to other issues with specs and lazy sequences, but a one-argument + behaves differently from two-arg one in lazy seqs with spec:

(println (reduce + 5 (map #(+ %) [3 4 "hi"])))

gives an unprocessed error message " Cannot cast java.lang.String to java.lang.Number", whereas two-arg + gives our modified class cast message neither gives a spec error, but that's a separate issue).