Question about gnu chess

[MGB]

HI all this my first post here

im brginner in chess programming , and when i run gnu chess in verbose mode it gave me the following

what does the + & . beside ply number means ???

Ply Time Eval Nodes Principal-Variation
1+ 0.02 41 1 Nf3
1. 0.02 41 21 Nf3
2& 0.02 -10 61 Nf3 Nf6
2. 0.02 -10 99 Nf3 Nf6
3& 0.02 40 203 Nf3 Nf6 Nc3
3. 0.02 40 222 Nf3 Nf6 Nc3
4& 0.02 -10 376 Nf3 Nf6 Nc3 Nc6
4. 0.03 -10 870 Nf3 Nf6 Nc3 Nc6

thanks

[PK]

The & sign means: the score and the principal variation are derived from a search that is not complete. Program knows how it is going to score Nf3 after searching it do depth 4, but it didn't check all the alternatives. The lines without the ampersand mean thet GNUchess didn't find anything better while searching to this depth.

In some positions You will get a couple of & lines before program reaches the non-& line.