HP42s first major program (Double Integral) Best way to approach?

[Werner]

Just one more thing:
EK has to test for input 1 and (1,0), so it has to be (never mind the step numbers):

Code:

42▸LBL "EK"
43 1
44 -
45 ABS
46 X=0?
47 GTO 00
48 1
49 LASTX
50 +/-
51 SQRT
52 STO+ ST Y
53 SQRT
54 STO+ ST X
55 XEQ "AGM"
56 PI
57 X<>Y
58 ÷
59 STO× ST Y
60 X<>Y
61 4
62 ÷
63 RTN
64▸LBL 00
65 99
66 1
67 RTN
68▸LBL "AGM"
69 LSTO "B"
70 ABS
71 SIGN
72 +/-
73 LSTO "T"

I added my start of AGM as well, shorter, and works for B=0

Cheers, Werner