Hi, I want to deduce n[v]=2*n-n[c]-2 from n[e]=1/2*(3*n[v]+n[c]) and n-n[e]+n[v]=1 Another words: I want to express n[v] in terms of other variables. But solve does't work this for me. What function should I use? -- Wang Yin DA Lab, Tsinghua University, 100084 Beijing China