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Ooops! Sorry, I send it only to Uwe Ligges the first time. Best, Philippe Grosjean This is perhaps another solution, more elegant in the way the block comment is written... but it requires to redefine `!` and slows it a little bit because it tests first its arguments before calling .Primitive(!): It takes advantage of `!` being not defined for character arguments: > !2 [1] FALSE >