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14. Compositions (Based on Hooks and Forks)

A verb is produced by trains of three or two verbs, as defined by the following diagrams:
```           FORK                 HOOK
g        g           g       g
/ \      / \         / \     / \
f   h    f   h       y   h   x   h
|   |   / \ / \          |       |
y   y   x y x y          y       y
```
For example, 5(+*-)3 (5+3)*(5-3) .

The foregoing definition is from Section II F of the dictionary. The following examples concern functions used in statistics:
```   mean=: +/%#                              Mean
norm=: ] - +/ % #                        Centered on mean
sqcm=: 2: ^~ ] - +/ % #                  Sqr of centred on mean
var =: [:    mean 2: ^~ ] - mean=: +/%#  Variance
stdv=: 2:%:[:mean 2: ^~ ] - mean=: +/%#  Standard Deviation

,.&.>@(];mean;norm;sqcm;var;stdv) y=: 2 3 4 5
+-+---+----+----+----+-------+
|2|3.5|_1.5|2.25|1.25|1.11803|
|3|   |_0.5|0.25|    |       |
|4|   | 0.5|0.25|    |       |
|5|   | 1.5|2.25|    |       |
+-+---+----+----+----+-------+

```

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