July 20 (Reuters) - The following are the top stories on the New York Times business pages. Reuters has not verified these stories and does not vouch for their accuracy.

* German Chancellor Angela Merkel reiterated her insistence that there be no reduction in Greek debt, but said other relief measures could be discussed. (http://nyti.ms/1Kfo5vX)

* For Greece, it's the economic equivalent of the Big Bang. So far, the questions about the tentative Greek bailout deal have focused on the pact's austere insistence on further cost cuts and new tax increases. But just as disruptive to Greek life could be the fundamental changes the pact is demanding in the cozy old ways that the country conducts business - changes meant to make Greece a more modern, efficient eurozone economy. (http://nyti.ms/1CKoeF8)

* Lockheed Martin has agreed to buy Sikorsky, the maker of the Black Hawk helicopters used by the United States military, people with knowledge of the matter said on Sunday. The deal, which one person said would be worth more than $8 billion, could be announced as soon as Monday. (http://nyti.ms/1JaDo7L)

* Next week, when Microsoft releases Windows 10, the latest version of the company's operating system, the software will offer a mix of the familiar and new to the people who run earlier versions of it on more than 1.5 billion computers and other devices. But Microsoft will not charge customers to upgrade Windows on computers, a shift that shows how power dynamics in the tech industry have changed. (http://nyti.ms/1HDGDCs) (Compiled by Supriya Kurane in Bengaluru)