Bug of the function "lift"

[koszulcomplex]

"lift" will give a warning when 2nd module does not lie in the first. However it does not work well when the 1st module is 0. Example:

> ring RING=0,(X,Y),dp;
> //This is normal:
. lift(ideal(X),Y);
   ? 2nd module does not lie in the first
   ? error occurred in or before STDIN line 2: `lift(ideal(X),Y);`
   ? wrong type declaration. type 'help ideal;'
> //The following are ridiculous:
. lift(ideal(0),Y);
_[1,1]=0
> lift(module(gen(10)),gen(11));
_[1,1]=-1
> lift(module(gen(10)),gen(12));
_[1,1]=0

[hannes]

handling of exceptional cases fixed (module being 0-module, or rk(mod) < rk(submod) etc.)