How do I close a gap

I deleted a clip and left a gap. I am having a problem closing the gap on the timeline. If I try to drag the following clip it springs back to its original position. If I select the gap with my mouse and find the duration, I can only reduce the gap to 1 not 0. If I press Delete, the gap remains. In FCE there was a Command -G which closed the gap, cannot finf one in in FCPX

What am I doing wrong?