\version "2.18.2"

%1) Implicit
{c'}

%2)  Explicit
\score {
  \new Staff { 
    \new Voice {c'}
  }
}

%3) Does run, using \with statement 
\score { 
   \new Staff 
     \with {  
        \override StaffSymbol.line-count = #0
      }  
   \new Voice {c'}
 } 
 
% 4)Generate error, using {} arround \with statement 
\score { 
   \new Staff {
     \with {  
        \override StaffSymbol.line-count = #0
      }  
   }
   \new Voice {c'}
 } 
 
% 5) Generate error, using << and >> arround \with statement 
\score { 
   \new Staff <<
     \with {  
        \override StaffSymbol.line-count = #0
      }  
   >>
   \new Voice {c'}
 } 
 
% 6) Does execute without \with statement and without voice
 \score { 
   \new Staff {
       \override Staff.StaffSymbol.line-count =  #0    
   }    
 }
 
% 7) Generate error, without \with statement 
 \score { 
   \new Staff {
       \override Staff.StaffSymbol.line-count =  #0
   }
   % generate unexpected \new
   \new Voice  {c'}   
 }