Simple vector operations. Like with built-in operations, should work
with both row and column vectors. I'll add more as I come up with
them.

<VEC: angle between two vectors
Inputs:
X, Y: Vector matrices

Outputs:
X: angle, in current mode


00 { 16-Byte Prgm }
01▸LBL "∡VEC"
02 UVEC
03 X<>Y
04 UVEC
05 DOT
06 ACOS
07 END



Original version of <VEC, written before I thought to normalize the
vectors. I'm keeping it around because it's the first nontrivial
function I made that only uses the stack and it was fun to write.
There was a second version where I used FNRM to get magnitude instead
of my own LVEC but let's not clutter.

00 { 42-Byte Prgm }
01 LBL "<VEC"
02 ENTER
03 XEQ "LVEC"
04 Rv
05 DOT
06 X<>Y
07 XEQ "LVEC"
08 R^
09 ×
10 /
11 ACOS
12 RTN
13 LBL "LVEC"
14 ENTER
15 DOT
16 SQRT
17 END