[TYPES] Historical question: origin of the ":" symbol

[Edsko de Vries]

Hi,

Can anyone refer me to a discussion of the history of the symbols used
in type theory? In particular, the origin of the ":" symbol? I seem to
recall reading somewhere that is derived from \epsilon, which in turn is
the first letter of 'esti' (to be), but I cannot remember where I read
this -- might have made it up myself :)

Thanks,

Edsko