Dear Neil! The first "modern" use of E! x F(x) I know is in Kleene's IM, p. 199. Best Panu Panu Raatikainen PhD., Docent in Theoretical Philosophy Fellow, Helsinki Collegium for Advanced Studies University of Helsinki E-mail: panu.raatikainen at helsinki.fi http://www.helsinki.fi/collegium/eng/Raatikainen/raatikainen.htm