$arg(z) \equiv \{ t \in \mathbb R : |z|e^{i (\pi/2)t} = z \}$

We plot the function here:
- Note that for every value $z \in C$, we get a
*set*of values associatedto it.

`right`

towards `bot`

,
arbitrarily stipulating ("picking a branch") that `arg(right) = 0`

as a sort
of basepoint.
- Note that we were
*forced*to pick the value`arg(bot) = -1`

from ourconsiderations of continuity. No other value extends continuous from theright to the bottom. - Also note that we got a
*smaller*value: we move from`0 -> -1`

: we decreaseour value as we move clockwise.

what happens if we move in the opposite direction?

- Let's move counter-clockwise from
`right`

, arbitrarily picking the branch`arg(right) = 0`

as before. This gives us:

- Note that once again, we were
*forced*to pick`arg(top) = 1`

by continuityconsiderations.

- Also note that this time, we got a
*larger*value: we move from`0 -> 1`

: weincrease our value as we move counter-clockwise

```
bot -> right -> top -> left -> bot -> right -> top -> left
-1 -> 0 -> 1 -> 2 -> 3 -> 4 -> 5 -> 6
```

That is, we end up with the value `6`

, which can only b
- Allowing multi-valued functions.
- Forcing continuity constraints.
- Interpreting increase/decrease in the value of the function.

- We are on the space of the spokes, given by
`a, b, c, d, e, f, g, h`

. - We have a function
`f: Spoke -> Val`

whose values are given on the spokes. - We are interested in the path
`p: Time -> Spoke`

,`p = [a, b, c, d, e, f, g, h, a]`

. - If we evaluate the function
`f`

on the path`p`

, we get`out: Time -> Val`

,`out = [0, 1, 2, 3, 4, 5, 6, 7, 0]`

. - We have a "jump" from
`7`

to`0`

in`out`

as we cross from`h`

to`a`

. This is adiscontinuity in`out`

at time`7`

. - We want to fix this, so we make the function
`f`

multi-valued.

- We assign both values
`8`

and`0`

to the spoke`a`

. We wish to definethe evaluation of`f: Spoke -> 2^N`

relative to path`p`

. At time`t`

, point`p[t]`

, we pick any value in`f(p[t])`

that makes`out[t]`

continuous.

- So in this case, when we start, we have two choices for
`out[0] = f(p[0]) = f(a)`

:`0`

and`8`

.But we know that`out[1] = f(p[1]) = f(b) = 1`

. Hence, for`out[0]`

to be continuous, we mustpick`out[0] = 0`

.

- Similarly, at
`out[8]`

we have two choices:`0`

and`8`

. But we have that`out[7] = 7`

, hence we pick`out[8] = 8`

.

- Note that we say 'we pick the value' that makes
`out`

continuous. This isnot really rigorous. We can fix this by re-defining`f`

in such a waythat`f`

is not`Spoke -> Val`

, but rather it knows the full path:`f': (Time -> Spoke) -> Val`

.

```
path: Time -> Spoke
f: Spoke -> 2^Val -- multi-valued
-- | morally, not mathematically.
out: Time -> Val
out t = choose_best_value (f(path[t]))
```

But there was a vagueness in this `choose_best_value`

. So we redefine it:
```
path: Time -> Spoke
f': (Time -> Spoke) -> Time -> Val
f'(path, tcur) =
argmax (\v -> |v - path[tcur-1]| + |v - path[tcur+1|)
f(path[tcur])
out: Time -> Val
out = f'(path)
```

- The function
`f'`

that defines the value of the path has fullaccess to the path itself! - At time
`tcur`

, it attempts to pick the value in`f(path[tcur])`

whichmakes the discontinuity as small as possible. It picks a value`v`

from thepossible values of`f(path[tcur])`

. This`v`

minimises the of the distances from the previous time point (`|v - path[tcur-1]`

), and the distance from the next time point (`|v - path[tcur + 1]`

). - This provides a rigorous definition of what it means to "pick a value in the branch".This can clearly be extended to the continuous domain.