## Position of element of list...

Hy

I have a list

A:=[[2,1],[1,2],[3,5],[7,6]]

I want to be able to tell what position the element [3,5] is in the list

I'm using

member([3,5],A,'t')

is there anything faster

maybe instead of storing as a list, I can use rtables or something?

## Wrong type inside a loop...

Eight matrices inside the list J:

J := [Matrix([[1, 0], [0, 1]]), Matrix([[0, -I], [-I, 0]]), Matrix([[0, -1], [1, 0]]), Matrix([[-I, 0], [0, I]]), Matrix([[-1, 0], [0, -1]]), Matrix([[0, I], [I, 0]]), Matrix([[0, 1], [-1, 0]]), Matrix([[I, 0], [0, -I]])];

Function member identifies J[2] as a member of J and returns its position in j:

member(J[2], J, 'j'); j;

Matrix multiplication inside a loop does not have a matrix type:

for i to 1 do for j to 2 do a := J[i].J[j]; member(a, J, 'k'); print(i, j, k, a, whattype(a)) end do end do;

Has anyone any ideia of what is going on?

## Subtract member from set...

I know how we can add a member to a mathematical set ,for example :

C := NULL;

C := C, V, B, X;

print(C)

V, B, X

but, my problem is that how we can subtract a member from the defined set ?

Thanks,

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