Solve without vars

*To*: mathgroup at smc.vnet.net*Subject*: [mg130347] Solve without vars*From*: juchheissassa at gmail.com*Date*: Wed, 3 Apr 2013 22:53:18 -0400 (EDT)*Delivered-to*: l-mathgroup@mail-archive0.wolfram.com*Delivered-to*: l-mathgroup@wolfram.com*Delivered-to*: mathgroup-newout@smc.vnet.net*Delivered-to*: mathgroup-newsend@smc.vnet.net

I happened to hit on the following curious thing: If I use Solve with {} instead of vars, I actually get a solution. Is this documented anywhere? What are the rules? e.g.: Solve[a x + y == 7 && b x - y == 1, {}] yields {{y -> 7 - a x, b -> (8 - a x)/x}} while Solve[a x + y == 7 && b x - y == 1, {x,y}] yields {{x -> 8/(a + b), y -> -((a - 7 b)/(a + b))}}