Cisco :: RFC 791 Widely-used Version Of Internet Protocol

The IP defined in RFC 791 was the first widely-used version of the Internet Protocol. Interestingly, however, it is not version 1 of IP but version 4! This would of course imply that there were earlier versions of the protocol at one point. Interestingly, however, there really weren't. As I mentioned above, IP was created when its functions were split out from an early version of TCP that combined both TCP and IP functions. TCP evolved through three earlier versions, and was split into TCP and IP for version 4. That version number was applied to both TCP and IP for consistency.url... what i wanna know s in tat underlined line its given 3 versions of TCP what r they?