User blog comment:Alejandro Magno/Make an extension of the notation 3 (WHAT IS BAD ABOUT BLOG POSTS VEL?!?!?!?!?!)/@comment-5029411-20141023231850

(a)[d] = {a,b,c,d}

(a)[d] = {a,b,c,d,e}

(a)[d] = (a)[d] with c b's