foo.cc:3:9: error: 'a' was not declared in this scope
    3 | int cmd(a,b)
      |         ^
foo.cc:3:11: error: 'b' was not declared in this scope
    3 | int cmd(a,b)
      |           ^
foo.cc:3:12: error: expression list treated as compound expression in initializer [-fpermissive]
    3 | int cmd(a,b)
      |            ^
foo.cc: In function 'int main()':
foo.cc:20:21: error: 'cmd' cannot be used as a function
   20 |  cout<<cmd(a,cmd(b,c));
      |                     ^
foo.cc:20:22: error: 'cmd' cannot be used as a function
   20 |  cout<<cmd(a,cmd(b,c));
      |                      ^

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