unitsize(1cm);

path  seg=(0,4)--(5,3); // définition d'un chemin (segment).
transform t=shift(0,-.8); // définition d'une translation.

DefaultHead=SimpleHead;

draw("$a$",seg,Arrow());
draw(Label("$b$",BeginPoint),t*seg,Arrow());
draw(Label("$c$",EndPoint,red),t^2*seg,Arrow());
draw(Label("$d$",EndPoint,red),t^3*seg,S,Arrow());
draw(Label("$e$",EndPoint,align=S,red),t^4*seg,Arrow());
draw(Label("$f$",align=LeftSide),t^5*seg,Arrow());
draw(Label("$g$",align=RightSide),t^6*seg,Arrow());
draw(Label("$h$",align=Center),t^7*seg,Arrow());
draw(Label("$i$",align=Center,UnFill),t^8*seg,Arrow());
draw(Label("$j$",Relative(.25)),t^9*seg,Arrow());
draw(Label("$k$",Relative(.75),blue),t^10*seg,.5green,Arrow());

shipout(bbox(2mm,white));