Xy-pic User's Guide

## 2.7 Arrows passing under

Arrows can pass under (or via) any other entry: Just insert `'`t, i.e., a quote (apostrophe) character followed by a target, for each entry that should be visited except the last, "ordinary & final" entry:

>     \xymatrix{
>      {\circ}
>       \ar@{|-->} '[dr] ^a
>                  '[rr]+D*{\bullet} ^b
>                   [drrr] ^c
>              & {\circ} & {\circ} & {\circ} \\
>      {\circ} & {\circ} & {\circ} & {\circ} }

typesets

As you see, labels are set separately on each segment.

#### Exercise 12.

Typeset the "lambda cube"

Hint: "going under" an empty entry leaves a small gap at that location. The compactness is achieved using a trick described in section 3.3.

Answer.

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