[O] problem with lookup, count several string in one (or more) columns.

[Uwe Brauer]

Hello

I tried to follow the instructions found in
http://orgmode.org/worg/org-tutorials/org-lookups.html

So I want to count all strings NP MH  in the following table
According to the instructions, the following will search the string MH.

| group | round 1 | round 2 |
|-------+---------+---------|
| A     |         |     2.4 |
| B     | 4.7     |      11 |
| C     |         |      MH |
| D     | 5       |         |
| E     |         |     7.2 |
| F     | 3.2     |     4.3 |
| G     | NP      |     4.4 |
| H     | NP      |       8 |
| I     | NP      |       8 |
|-------+---------+---------|
| total | MH      |       1 |
#+TBLFM: @>$3='(length(org-lookup-all "MH" '(@address@hidden) nil));

So I could repeat that for the string NP as well but how can I search
for both (or more) strings at once?