assert_invariants( self ); 
void string_push_back( string* self, char x ){    assert_invariants( self );    string_append_range( self, &x, &x + 1 );    assert_invariants( self );}
2658	/local/tlutelli/issta_data/temp/c/2005_temp/2005/2658/afcd1ca78eb4d69e13f7f7bc1df43b45af487b65/strings.c/clean/src/engine/strings.c