Unresolved conflict for symbol sequence:

  expression  '+'  expression  •  '+'  …

Possible interpretations:

  1:  (math_operation  expression  '+'  expression)  •  '+'  …
  2:  expression  '+'  (math_operation  expression  •  '+'  expression)

Possible resolutions:

  1:  Specify a left or right associativity in `math_operation`
  2:  Add a conflict for these rules: `math_operation`