foo.cc: In function 'int p(int, int)':
foo.cc:12:10: error: 'b' was not declared in this scope
   a.push(b[i]);
          ^
foo.cc: In function 'int main()':
foo.cc:45:10: error: 'fas' was not declared in this scope
      tot=fas(i-j);
          ^~~
foo.cc:45:10: note: suggested alternative: 'ffs'
      tot=fas(i-j);
          ^~~
          ffs

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