I made a code which draws a plot of $5-x^2$ masked with a kind of `rectangular function`

in order to brake the branches of parabola at the points `-1`

and `1`

and transform them into a vertical lines.

```
Clear("Global`*")
rgbC = RGBColor(0.880722, 0.611041, 0.142051);
pltS = {rgbC};
f = 2 - Abs(Abs(-1 + x) - Abs(1 + x));
(*triangular function with height 2 and base 2*)
lin = 2 -
Abs(2 x); (*auxiliary function to make rectangular function of
triangular function*)
k = FullSimplify(
lin/f); (*rectangular function with height 1 and base 2, defined
on intervals x(-1,1) and y(1,-(Infinity))*)
eq1 = x^4;
eq2 = 5 - x^2 + k - 1;
fPlt = {Plot(I*x, {x, -2, 2}, AspectRatio -> Automatic,
PlotRange -> {{-2, 2}, {0,
5}})}; (*empty 'canvas' for applicating combined mPlt and uPlt*)
mPlt = {Plot({eq1}, {x, -3, 3}, Method -> "BoundaryOffset" -> False,
AspectRatio -> Automatic, Filling -> Top,
FillingStyle -> LightBlue, PlotRange -> {0, 3})};
uPlt = {Plot({eq2}, {x, -1.1, 1.1}, Method -> "BoundaryOffset" -> False,
PlotStyle -> {pltS}, PlotRange -> {{-2, 2}, {3, 5}},
Filling -> Bottom, FillingStyle -> LightYellow)};
Show(fPlt, mPlt, uPlt)
```

The code works as expected when $x$ in `uPlt`

varies from `-1.1`

to `1.1`

:

But things go curiouser when $x$ is bounded by `-1`

and `1`

, the vertical lines desappear:

And it all becomes curiouser and curiouser with $x$ is ranging from `-2`

to `2`

, now the only left “leg” is absent. The circumstances are aggravated by the error message ‘infinite expression 1/0 encountered’ popping:

Both legs are gowing back again with `{x,-2,3}`

or `{x,-3,3}`

and the error message persists.

What is going on?