PARIS — France’s state-controlled power company challenged a proposed takeover by Warren Buffett of Constellation Energy Wednesday, putting up almost as much money for half its nuclear business as the legendary Nebraska investor had offered for the entire company.

Constellation shareholders have already filed at least half a dozen lawsuits, saying the $4.7 billion bid from Buffett’s MidAmerican Energy Holdings Co. was too low. MidAmerican swept in to acquire the company three months ago as Constellation wrestled with frozen credit markets and tried to stay afloat.

Electricite de France SA, Constellation’s biggest shareholder, offered $4.5 billion for just half of the U.S. wholesale power generator’s nuclear business early Wednesday.

Cyber Monday sales better than expected

Wooed by heavy discounts from online retailers, consumers who had been exercising restraint during this young holiday shopping season finally let themselves go on Cyber Monday. E-commerce spending on that day, the first workday after the long Thanksgiving weekend, jumped 15 percent to $846 million, according to a ComScore report released Wednesday morning.

This provides much-needed relief for online merchants, which saw sales drop 2 percent in November — the first such decline after years of double-digit increases. But retailers might have had to slash away at their profit margins to get consumers buying.

“Consumers are clearly responding positively to retailers’ aggressive online discounts. With Cyber Monday promotions beginning in earnest over the Thanksgiving weekend, consumers have finally begun to open their wallets,” ComScore Chairman Gian Fulgoni said. “This is an extremely encouraging development for retailers and we can but hope that their aggressive discounting still has left room for profits.”