Close Polyline
Sketch > Process > Trim 
> Close polyline 
This function closes open polylines of sketches, i.e. start and end point of the polyline will be connected by means of a new line.
Move the cursor near an edge of the polyline you want to close. If a closing of the polyline is possible, a preview image will be displayed.
Apply the connection with a left-click. The function remains active, i.e. you can close further polylines if desired. Press the middle mouse button to exit the function.
Right-click to open a context menu with the following function:
                                 
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                                 Cancel Cancels the function without applying the changes.  | 
                        
Polylines of non-active sketches can also be closed with this function. The created new connecting lines always belong to the processed sketch.
                
            
                            