connected sum
The connected sum of knots and is a knot, denoted by ,constructed by removing a short segment from each of and and joining each free end of to a different free end of to form a new knot. The connected sum of two knots always exists but is not necessarily unique.
The connected sum of oriented knots and is a connected sum of knots which has a consistent orientation inherited from that of and . This sum always exists and is unique.
Example.
Suppose and are both the trefoil knot.
By one choice of segment deletion and reattachment, is the quatrefoil knot.