The phrase "a very very extensive" is correct and usable in written English.
It can be used to emphasize the degree of extensiveness of something, often in informal contexts.
Example: "The report provided a very very extensive analysis of the market trends over the past decade."
Alternatives: "a highly extensive" or "an extremely extensive".
"This is a very, very extensive investigation," Ralf Möllmann, a prosecutor in Düsseldorf, Germany, said.
"There is a very, very, extensive security and intelligence presence everywhere in Aleppo and they crack down on any protest as soon as it starts," he said.
"We've been at this for the last three years, and it was a very, very extensive amount of work with a lot of players in the industry".
Ross D. Levi, the executive director of the Empire State Pride Agenda, said: "The states that have passed either marriage or civil unions have a range from either nothing — Iowa and Massachusetts have no religious exemptions — to very, very extensive, and I think what the governor is working on is finding that balance.
Feynman spent a large portion of his Nobel Prize lecture detailing how Wheeler had spent very, very extensive periods of patient time with Feynman, correcting all of the assumptions and approaches that he took in that work that eventually won Feynman a Nobel Prize.
"Looking at the damage, we are a bit surprised we don't have more injuries and/or fatalities, because some of the damage is very, very extensive," he said.
The documents were sort of political debates, magazines, and so on and so forth because of the state control of the media was very, very extensive but into Hungry I would also take in Xerox machines so they could copy material and distribute it in Budapest.
"It's a very, very time-extensive product to make," said Craig Brommers, director of sports marketing for Speedo.
A very, very surreal moment".
"A very, very long while".
"It's a very, very, very, very, very great experience.
