@Ronan 
Do you understand this ? : savelibname := "C:/Users/jando/Maple/toolbox/Cliffordlib":
 .ini file is located in Maple folder  in this path ( sorry.  i was not clear enough) 

The nest step is the package "mapel.ini" file needs to be placed in "C:\Program Files\Maple 2026\Users". : 
It seems that the ini file is outside Maple program itself. 

I am on Windows 11 pro and use now Maple 2026.1, this seems to work for me 

Users this map 

@Ronan 
Yoy can do it with this ?

savelibname := "C:/Users/jando/Maple/toolbox/Cliffordlib":
libname := savelibname, libname:

read cat(savelibname, "/define.m"):
read cat(savelibname, "/definemore.m"):
read cat(savelibname, "/Walshpackage.m"):

 .ini file is located in Maple folder
Cliffordlib is name of package 

Maple 2026.1

@Ronan 
Its working on Windows 11 pro 

Pattern  from triangle (not a euclidian)  and twincircles?

UHG_module_2D_-_6-9-2026.mw

a non-periodic function

@Kitonum 
Note that the planes are positioned perpendicular to each other, so this requires additional code.and other  things in a earlier example, so  i don't see your point  ? 
No textplots are possible with draw and display.commands.
 

restart:
with(geom3d):
plane(P1,x+y=1,[x,y,z]):
plane(P2,x-y=2,[x,y,z]):
point(A,1,0,0):
point(B,2,0,0):
intersection(L,P1,P2):
draw([P1(color=blue,transparency=0.55,style=surface),P2(color=yellow,transparency=0.55,style=surface),L(color=black,thickness=4),A(color=red,symbol=solidsphere,symbolsize=16),B(color=red,symbol=solidsphere,symbolsize=16)],axes=boxed,labels=[x,y,z],scaling=constrained,view=[-3..5,-4..4,-3..4],orientation=[55,65],title="Two Planes using geom3d");

Its a lot of work to do this with geom3d 

@erik10 
I looked into what you asked in even more detail and am using only the geom3d package here, but a different approach using a linear algebra package is also possible
My investigation..
twee_vlakken_volledig_via_geom3d_pakket_30-8-2026.mw

restart:
with(geom3d):
plane(P1,x+y=1,[x,y,z]):
plane(P2,x-y=2,[x,y,z]):
Equation(P1);
Equation(P2);
n1:=NormalVector(P1);
n2:=NormalVector(P2);
n1;
n2;
ArePerpendicular(P1,P2);
alpha_oriented:=FindAngle(P1,P2);
alpha:=abs(alpha_oriented);
alpha_deg:=simplify(alpha*180/Pi);
alpha_oriented;
alpha;
alpha_deg;
point(A,1,0,0):
point(B,2,0,0):
coordinates(A);
coordinates(B);
IsOnObject(A,P1);
IsOnObject(B,P2);
intersection(L,P1,P2):
detail(L);
point(Au,2,-1,0):
point(Av,1,0,1):
dsegment(U1,[A,Au]):
dsegment(V1,[A,Av]):
point(An,2,1,0):
dsegment(N1,[A,An]):
point(Bu,3,1,0):
point(Bv,2,0,1):
dsegment(U2,[B,Bu]):
dsegment(V2,[B,Bv]):
point(Bn,3,-1,0):
dsegment(N2,[B,Bn]):
point(Q,3/2,-1/2,3/2):
h:=1/3:
point(Q1,3/2+h,-1/2-h,3/2):
point(Q2,3/2+h,-1/2+h,3/2):
point(Q3,3/2+2*h,-1/2,3/2):
segment(RA1,[Q1,Q3]):
segment(RA2,[Q2,Q3]):
draw([P1(color=blue,transparency=0.55,style=surface),P2(color=yellow,transparency=0.55,style=surface),L(color=black,thickness=4),A(color=red,symbol=solidsphere,symbolsize=16),B(color=red,symbol=solidsphere,symbolsize=16),U1(color=red,thickness=4),V1(color=green,thickness=4),N1(color=black,thickness=4),U2(color=red,thickness=4),V2(color=green,thickness=4),N2(color=black,thickness=4),RA1(color=red,thickness=6),RA2(color=red,thickness=6)],axes=boxed,labels=[x,y,z],scaling=constrained,view=[-3..5,-4..4,-3..4],orientation=[55,65],title="Perpendicular Planes using geom3d");

special_first-order_resultaat_modigeficeerde_Besselverg_2_e_orde_afleiding_28-6-2026_def.mw

For n = 1, the formula has been numerically verified 
Now by complete induction ....

This should be the solution sequenze for the modified Bessel function at the bottom

@dharr 
More to find 

@dharr 
This is ..

@Ronan 
The code works with all the points you mentioned.