end1 4.0

end1

This is a built-in link variable. It indicates the first endpoint (turtle) of a link. For directed links this will always be the source for undirected links it will always be the turtle with the lower who number. You cannot set end1.

crt 2
ask turtle 0
[ create-link-to turtle 1 ]
ask links
[ show end1 ] ;; shows turtle 0