|Sketch → Sketcher tools → Connect Edges|
|Introduced in version|
Applies Coincident constraints to endpoints with the same coordinates of the selected elements.
Select the elements in the 3D-view or in the listbox on the left side of the screen and click on the icon.
Before using this command make sure that obvious constraints (horizontal, vertical, tangential) are already applied to the elements. Selecting the elements in a counter-clock-wise order seems to produce better results.