 One first proves Serge Lang's theorem, stating that the analogous theorem is true for the field F"p"(("t")) of formal Laurent series over a finite field F"p" with formula_1.In other words, every homogeneous polynomial of degree "d" with more than "d"2 variables has a non-trivial zero (so F"p"(("t")) is a C2 field).Then one shows that if two Henselian valued fields have equivalent valuation groups and residue fields, and the residue fields have characteristic 0, then they are elementarily equivalent (which means that a first order sentence is true for one if and only if it is true for the other).