[Dev-luatex] variable

Hello, Anybody know how I can set variable in tex? For example \count10=20 \def\proste{To jest prosty napis} a\directlua{tex.print(tex.count[10]+5)}b a\directlua{tex.set("\proste","Trudne")}b \proste \bye I need setup \proste definition to my own string How I can read TeX variable \mynumber from lua and set variable \mynumber on TeX but set in lua script. Thanks Janusz Biznesu