2D implicit curve

### 3.10.1 2D implicit curve

- `plotimplicit(f(x,y),x,y)` draws the graphic representation of the curve defined by the implicit equation f(x,y)=0 when x (resp y) is in `WX-, WX+` (resp in `WY-, WY+`) defined by `cfg`,
- `plotimplicit(f(x,y),x=0..1,y=-1..1)` draws the graphic representation of the curve defined by the implicit equation f(x,y)=0 when 0≤ x ≤ 1 and −1≤ y ≤ 1

It is possible to add two arguments to specify the discretisation steps for x and y with `xstep=...` and `ystep=...`.
Input :

`plotimplicit(x```^```2+y```^```2-1,x,y)`

Or :

`plotimplicit(x```^```2+y```^```2-1,x,y,unfactored)`

Output :

`The unit circle`

Input :

`plotimplicit(x```^```2+y```^```2-1,x,y,xstep=0.2,ystep=0.3)`

Or :

`plotimplicit(x```^```2+y```^```2-1,[x,y],xstep=0.2,ystep=0.3)`

Or :

`plotimplicit(x```^```2+y```^```2-1,[x,y], xstep=0.2,ystep=0.3,unfactored)`

Output :

`The unit circle`

Input :

`plotimplicit(x```^```2+y```^```2-1,x=-2..2,y=-2..2, xstep=0.2,ystep=0.3)`

Output :

`The unit circle`