arg1 = scm_sym2vcell (x, scm_env_top_level (env), SCM_BOOL_F);
SCM_ASSYNT (SCM_NFALSEP (arg1) && !SCM_UNBNDP (SCM_CDR (arg1)),
x, "variable already unbound ", s_undefine);
arg1 = scm_sym2vcell (x, scm_env_top_level (env), SCM_BOOL_F);
SCM_ASSYNT (SCM_NFALSEP (arg1) && !SCM_UNBNDP (SCM_CDR (arg1)),
x, "variable already unbound ", s_undefine);