Why does _EnvLinalg95 only affect  (and ) and not and ? 
 

Download _EnvLinalg95.mw

I have read the help page of Eigenvectors but couldn't find anything related.

There seems to be a consensus about using ListTools:-SearchAll to locate an item in a list. However, this subroutine does not work on other expressions; A simple instance is that “ListTools:-SearchAll(1, [[1], 1]);” only outputs  while what I need is  (because both “op([1, 1], [[1], 1])” and “op([2], [[1], 1])” are ). And actually, I hope that there is a more general version in Maple.
For example, I intend to do something like 

restart;
expr, elem := ToInert(eval(`print/Diff`)), '_Inert_NAME'("_syslib"):
SearchAll(elem, expr);

and 

List:=[[[[cS,[[[cS,cS],cS],[[[cS,cS],[[cK,cK],cS]],cS]]],cS],cS],[[[cS,[[cK,cS],cK]],cK],cS]]: 
items:=Or([[[identical(cS),anything],anything],anything],[[identical(cK),anything],anything]): 
SearchAll(items,List); 

In other words, I need all positions of an operand of an expression (cf. op).

It may be manually checked that the "indices" of  in  include [5,1,1,2,1,1,1,2,1,2,1,2], [5,1,2,2,1,1,1,1,2,1,2], and [5,2,2,1,1,3,1,2], since 

patmatch(op([5, 1, 1, 2, 1, 1, 1, 2, 1, 2, 1, 2], expr), elem);
 = 
                              true

patmatch(op([5, 1, 2, 2, 1, 1, 1, 1, 2, 1, 2], expr), elem);
 = 
                              true

patmatch(op([5, 2, 2, 1, 1, 3, 1, 2], expr), elem);
 = 
                              true

Similarly, after some manual searchs, 

[[1], [1, 1, 1, 2], [1, 1, 1, 2, 2], [1, 1, 1, 2, 2, 1, 2], [2], [2, 1, 1, 2]]:
convert(typematch~(map2(`?[]`, List, `%`), items), `and`);
 = 
                              true

It turns out that all "indices" in  of  are [1], [1,1,1,2], [1,1,1,2,2], [1,1,1,2,2,1,2], [2], and [2,1,1,2].
But isn't there such a  command that can eliminate the need to manually retrieve them?

In an old question, @nm asked how to . While the answer in that question was almost up to the mark, there remains a regret. 

As the instance listed below shows, Maple, by default, draws arrows on a rectangular grid (rather than on a hexagonal mesh): 

  # Example of a three-dimensional vector field: 
vf__2d := VectorCalculus:-VectorField([sin(x)*(cos(x) + cos(y)), 
                                       sin(y)*(cos(x) - cos(y))], 'cartesian'[x, y]):
  # Example of a two-dimensional vector field: 
vf__3d := VectorCalculus:-VectorField([1 - (sin(u - v) + sin(u - w)), 
                                       1 - (sin(v - w) + sin(v - u)), 
                                       1 - (sin(w - u) + sin(w - v))], 'cartesian'[u, v, w]):
  # Phase portrait. 
Student:-VectorCalculus:-PlotVector(vf__2d, (x, y) =~ -Pi .. Pi, 
                                            'grid' = [`$`](25, 2), 
                                          'arrows' = 'THICK', 
                                   'fieldstrength' = log[63], 
                                           'color' = ColorTools:-Color("#0072BD"), 
                                            'axes' = "box"(*, …omitted…*));
= 

Note that I have changed some of the options in order to make the layout of arrows more prominent.
However, according to the help page of Mma's VectorPoints, among the following methods of location generation, Mma by default uses Hexagonal for 2D field vectors and FaceCenteredCubic for 3D field vector: 

, 

Here is a collection of different settings available in Mma:

So if the requirement is to get the Maple's output looking like Mathematica's (see the beginning), the number and placement of vectors to plot should be thought of as well. In Maple, “the number of vectors” can be controlled by the plot (or plot3d) opinion , but how do I specify “the placement of vectors” (e.g., Mma's "Hexagonal" and "Mesh")?

Although there exists an  chapter in the documentation, randomly positioned arrows do not fit the bill. Is there any workaround?

This question is an expansion of my previous reply. 

There exist sixty kinds of statements in Maple, whose major ​​​​portion can be used as an expression or within an expression (e.g., assignment, loop, and condition). But why is use an exception?

Moreover, since it is reasonable to think of use as a (partial) generalization (see below) of the subs function, shouldn't the behaviour of use be consistent with do/if?

Edit. Besides that, is there some workaround to do something like

  # If use can be used as an expression or within an expression, 
use x = 2 + y in 'use y = 4 in x + y end' end;
  # should return “use y~ = 4 in (2 + y) + y~ end use;” and 
(use y = 2 + x in x -> x + y end);
  # should output “x~ -> x~ + (2 + x);”. 
  # Unfortunately, I cannot find a workaround to stimulate them.

 at present? Note that the `subs` function is unable to do so, so in my opinion, only when the use of `use` is no longer limited to statements will it become a sweeping generalization of `subs`.

The documentation says:

So “_” can be treated as an argument placeholder in a for–in loop. Nevertheless, I would like to know if there is an argument placeholder like MatLab's tilde (~) operator:

• Ignore Function Outputs
• Ignore Inputs in Function Definitions

Ordinarily, there is no need to to ignore inputs in function definitions, but as for the former, since there is a _nresults keyword in Maple (and some "built-in" routines do use it), when accessing the source code is unavailable, how do I ignore specific outputs from such a function (e.g., a procedure with option encrypted that has been loaded from a repository)?
For instance, the help page of MTM:-eig mentions three calling forms: 

1. l := MTM:-eig(A): 
2. [V,L] := MTM:-eig(A): 
3. [V,L,N] := MTM:-eig(A): 

If I do not directly invoke the linalg/Student[LinearAlgebra]/LinearAlgebra/Matlab package (and do not manually compute Eigenvals), will it be possible to imitate MatLab's 

[~, ~, W] = eig(A);

in Maple as verbatim as possible? 
Note that MatLab's help page claims: