> E1 := x - 2*y + z = 3:
> E2 := -x + 4*y = -1:
> E3 := 2*x + 4*z = 12:
>
> solve({E1,E2,E3},{x,y,z});
This produces no output. In fact, we can see that these equations are incompatible.
> B1 := E1 + E2;
B1 := 2 y + z = 2
> B2 := E3 - 2*E1;
B2 := 2 z + 4 y = 6
> 2*B1 - B2;
0 = -2
Which is a contradiction!