Early indications suggest that Wall Street stocks may open on a nervous note on Tuesday, with futures indicating a narrowly mixed opening. With the Greek euphoria fading and worries concerning the practicalities of the deal surfacing, traders could be on the back foot. The retail sales report for June due shortly ahead of the market open and earnings reports of Johnson & Johnson (JNJ), Wells Fargo (WFC) and JP Morgan (JPM) may also serve to accentuate the anxiety. Oil is extending the sell-off as Iran and the Western nations inch towards a deal on the former’s nuclear program.