[NTG-context] Hiding a part of a path

Dear all, I’d like to hide a part of a path. I can do that after changing it into an image, but it is not clearly erased. Is there a way to do that not changing it into an image? Thank you for reading. Best regards, Dalyoung \startMPcode path p,q; picture pic; numeric u; u:= 1cm; p := origin--(2u,0)--(3u,u)--(3u,0)--(4u,0); q := (3u,u)--(3u,0); pic := image(draw p; draw q withcolor white;); draw pic; \stopMPcode